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9 th 








■ ■ 

The complete and indispensable 
guide for the amateur astronomer 
both for the beginner and 
the experienced observer 

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v ^ v « 





The Amaleu) Axtronomei remains Patrick 

Moore's major contribution to the field of 
practical astronomy. He has brought to it 
all his experience of observing the sky 
for many years with equipment that is 
available to the amateur and - not least ■- 
of helping others 10 engage in this reward- 
ing activity. It is essential reading for the 
beginner who knows nothing whatsoever 
but who is, nevertheless, anxious to make 
a start with what equipment he can 
collect at limited cost; but it will also 
meet the needs of a great many amateurs 
who possess a telescope and need guidance 
as to the work they can do. 

The aim of" die book is to explain the 
basic facts as clearly and as simply as 
possible, as well as indicating some lines 
of work which can be undertaken by the 
amateur who wants to make himself useful 
to others. Here is the answer to the 
question, "If I want to make a hobby of 
astronomy, how do 1 set about" it?" 

It is written and organized for ease of 
reading and speed of reference. It 
discusses the problems of the amateur 
and his equipment. It provides a course 
in the nature of the skies, the solar system, 
the stars and the universe. It contains 
maps, charts and tables needed by the 
observer, together with a large number of 
diagrams and sixteen pages of half-tone 
photographs. In fact, it is the complete 
and indispensable guide for the amateur 
astronomer both the beginner and the 
experienced observer - who will find here 
a mass of detailed and invaluable advice. 

(Completely Revised) 

ISBN O 7188 2148 3 



The Amateur Astronomer's Library: 

vol I. the amateur astronomer, by Patrick Moore 

vol iv. practical amateor astronomy, edited by Patrick 

vol V. naked eye astronomy, by Patrick Moore 




PATRICK MOORE o.b.e,,f.r.a. s . 


First published 1957 
Second revised edition, 1958 
Third revised edition, i960 
Fourth revised edition, 1 961 
Fifth revised edition, 1 964 
Sixth revised edition, 1 967 
Seventh revised edition, 1971 
Eighth revised edition, 1 974 
Ninth revised edition, 1978 




Acc, No. 



3o A -->1 dl.fc 

Class No. 



ISBN o 718S 1 81 5 


Revised editions copyright (§) 1960, 1961, 1964, 1967, 1971, 1974, 1978 


Printed and bound in Great Britain at 
The Cametot Press Ltd, Southampton 



Foreword to the First Edition 

Forewords to the Seventh and Ninth Editions 


















I Planetary Data 
II Satellite Data 
III Minor Planet Data 














IV Elongations and Transits of the Inferior Planets 2 1 2 
V Map of Mars 2 15 



VI Oppositions of Planets, 1 970- 1 980 216 

VII Jupiter: Transit Work 217 

VIII Saturn: Intensity Estimates 219 

IX Recent and Forthcoming Eclipses 220 

X Artificial Satellites 222 

XI The Limiting Lunar Detail visible with 
Different Apertures 

XII The Lunar Maps 

XIII Some of the More Important Periodic Comets 239 

XIV Some of the More Important Annual Meteor 


XV The Constellations 

XVI Proper Names of Stars 

XVII Stars of the "First Magnitude" 

XVIII Standard Stars for Each Magnitude 

XIX The Greek Alphabet 

XX Stellar Spectra 

XXI Limiting Magnitudes and Separations for 
Various Apertures 

XXII Angular Measure 

XXIII Test Double Stars 

XXIV Extinction 
XXV Naked-eye Nova; 

XXVI Messier's Catalogue of Nebulae and Clusters 

XXVII The Star Maps 

XXVIII The Observation of Variable Stars 

XXIX Radio Astronomy 

XXX Amateur Observatories 

XXXI Astronomical Societies 

XXXII Bibliography 









Many popular books upon astronomy have been written 
during the past few years, but most of them cater either for the 
casual dabbler who is content to learn from the depths of his 
armchair, or else for the serious amateur who already knows the 
main facts. What I have done, or tried to do, is to strike a happy 
mean. This book has been aimed at the needs of the beginner 
who knows nothing whatsoever, but who is nevertheless anxious 
to make a start with what equipment he can collect at limited 

All astronomers, professional or amateur, were beginners 
once, and aU have had to draw upon the experience of those 
who have learned before them. I feel some diffidence about 
offering myself as a guide, but at least I have one qualification: 
in my early days as an observer I made almost every mistake 
that it is possible to make ! This explains the frequent occurrence 
of such phrases as "I once saw ..." and "I remember that when 
I ..." I hope, therefore, that what I have written may prevent 
others from falling into the same ridiculous traps. 

A common fault in popular books is that too much space is 
devoted to the Moon and planets, and too little to the greater 
problems of the stars. I am well aware that I have laid myself 
open to precisely this criticism, but there is a reason for it. I 
repeat that I am writing for the amateur who wants to observe j 
and while the owner of a small telescope can make himself 
extremely useful in the lunar and planetary field, he is rather 
more limited with regard to stellar problems. I hope, therefore, 
that the fault may be forgiven. 

It will be noticed that all the photographs and drawings in 
this book are the results of amateur work. 

I have said little about space-travel, a subject very much 
in the public eye to-day. This is not because I am sceptical 
about it; on the contrary. But to enlarge this book any further 
would have been to make it over-long, and space-travel prob- 
lems are beyond its scope. 

Much has been glossed over, and much has had to be left 
out. I have referred to instruments such as spectroscopes and 



micrometers, but the space available has not permitted me to 
describe them properly or to give comments upon how to make 
use of them ; nor have I given precise positions of the various 
stellar objects listed in the Appendix, while radio astronomy 
has been barely mentioned. If this book has a use, it will be to 
the man who works with cheap and limited equipment. I 
have, however, given a list of more advanced works which can 
be consulted by anyone who wants to go more deeply into the 

Astronomy is the most satisfying of all hobbies; taken as a 
class, astronomers are friendly folk. If my book persuades a 
few people to take a real interest in the heavens, I shall feel 
that it has been well worth writing. 


August JQJ7 



When the first edition of this book appeared, the Space 
Age had not begun : artificial satellites and probes to the planets 
still lay in the future. Moreover, the great Jodrell Bank radio 
telescope, now so celebrated all over the world, was barely in 
use. The advances made since then have been quite remarkable, 
and when I looked through the third edition of my book a day or 
or two ago I was reluctandy compelled to class it as something 
of a museum-piece. In no previous period of astronomical 
history would a period of only ten years have made so much 
difference — apart perhaps from the early part of the seventeenth 
century, when Galileo used his first telescope and Kepler 
formulated the Laws of Planetary Motion. 

I made revisions for the next few editions, but the last of these 
was published in 1967, and a great deal has happened since 
then. Most important of all, men have landed on the Moon. 
This means that a large part of the lunar chapter as printed in 
1967 is now out of date, even though at least some of the fore- 
casts I made then have been borne out by subsequent events. 
(Unkind people may say that this was more by luck than by 

Progress is now so rapid that one is always apt to be overtaken 
by sudden revolutionary discoveries. This may well happen in 
the present instance. If so, I can only plead that I have made 
the text as up to date as possible at the time of writing: 
December 1970, 

For this edition, I have added a section about the observation 
of variable stars, which is becoming an increasingly popular 
field of research for amateurs. I have also enlarged and extended 
the sections dealing with southern stars, so that the book now 
applies to countries such as Australia and South Africa as well 
as to Europe and the United States. 

I have had help from many friends and colleagues. The orig- 
inal manuscript of the first edition was checked by the late 
Rev. M, Davidson, Roger Griffin, W. M. Lindley, James Paton, 
G. A. Ronan, E. A. Whitaker, H. Wildey, and the late F. J. 


Sellers and M. B, B. Heath, all of whom read through various 
parts of it; R. A. Tyssen-Gee read through the entire set of 
proofs, a task which took him many hours, and made invalu- 
able comments and suggestions. Help in proof-reading was also 
given by Peter J. Cattermole. 

The plates have now been revised, and I am most grateful 
to those who have allowed me to use their drawings and 
photographs: Henry Brinton, F. L. Jackson, G. A. Hole, H. E. 
Dall, Commander H. R. Hatfield, T. W. Rackham, Paul 
Doherty, W. Rippengale, J. Paton, W. A. Granger, F. Acfield, 
R. E. Roberts, T. J. C. A. Moseley, Dr. H. R. Soper and H. 
Miles. New diagrams (fig. nos. 29, 34, 41 and 49) have been 
prepared by David Hardy, who also drew the Map of Mars 
(Appendix V), and by Lawrence Clarke. Finally, I must on no 
account omit to thank the publishers, and in particular Michael 
E. Foxell, for all that they have done. 

I must stress that any errors or deficiencies in the book are 
to be placed solely at my door, and that nobody else can be 
held responsible for them in any way. Meanwhile, to all those 
who have given up so much time to help me, I can only say- 
thank you. 

\^ December j, /070. 



Some extra revisions have been made, mainly to incorporate 
new research— in particular with respect to Mars. The basic 
plan of the book remains, of course, unaltered. 

February ij } iqjB 



(Plates I and II between pages 152 and 153) 


A. Henry Brinton's 12-in. equatorially mounted 

B. The author's i2^-in. altazimuth mounted reflector 

C. The rotatable head of Henry Brinton's reflector 


A. J. Hedley Robinson's run-off shed and revolving 

B. The author's observatory with revolving roof 

C. The author's run-off observatory at Selsey 

(Plates III to XIV between pages 160 and 161) 


Sunspots A. 1959 August 29 

B. i960 November 10 

C. 1 961 July 1 


A. Mare Imbrium 

B. Ptolemseus to Walter 

C. East Part of Mare Crisium 

D. Hyginus Cleft Area 


(left) Partial eclipse of the Sun, 1954 June 30 
(right) Total eclipse of the Moon, 1954 January 19 


A. Mars, 1965 March 9 

B. Jupiter, 1963 December 7 

C. Jupiter, 1964 August 23 



VII. (coat.) 

D. Jupiter, 1966 October 11 

E. Saturn, 1963 August 7 

F. Saturn, 1966 August 26 


A. Jupiter, 1963 November 2 

B. Jupiter, 1962 July 30 

C. Jupiter, showing Transit of Ganymede, 1963 
September 28 

D. Jupiter, showing Shadow Transit of Io, 1963 
October 27 

E. Saturn in 1957 




XII. the pleiades (Reproduced by the courtesy of R. E. 
Roberts and the Swansea Astronomical Society) 



XV. the moon: eastern half— -facing page 226 
XVI. the moon: western half- facing page 227 


Chapter One 


The twentieth century is the Age of Science. Since 
our grandparents were children, mankind's way of life has 
changed beyond all recognition, and if we could visit the world 
of a hundred years ago it would seem almost like being taken to 
another planet. The idea of a car, an aeroplane or a wireless 
set would have seemed fantastic to the average mid- Victorian, 
and even less would he have been prepared for some of the 
new scientific branches of to-day, such as nuclear physics and 

One result of this amazing progress is that science has become 
specialized. It used to be possible for the amateur to make useful 
discoveries, while to the normal research worker the possibilities 
were unlimited. There was always something new "just round 
the corner", and any apparently trivial experiments could 
open up new avenues. Such were Becquerel's casual studies of 
the behaviour of a lump of uranium in a darkened cupboard, 
which paved the way for the study of radioactivity and a 
method of treating the dread disease cancer. Now, however, 
the day of the amateur is largely done. Modem research cannot 
be carried out without equipment which is so expensive that it 
can never be assembled by any one man; even theoretical work 
is beyond the non-specialist. 

Astronomy is the one science in which these limitations are 
not so crippling. The chances of making an important dis- 
covery are less than they were at the start of the century, but 
they still exist. For instance, W. T. Hay — better known as Will 
Hay, the stage and screen comedian — was the first to see the 
white spot which appeared on Saturn in 1933, and in the follow- 
ing year a bright "new star" was discovered by another British 
amateur, J. P. M. Prentice. More recently other amateurs have 
made discoveries of exploding stars; George Alcock, from 
Peterborough, has found four, to say nothing of four comets. 
There is plenty of scope. 

It is obvious that there are some branches of astronomy 



which cannot be tackled by the amateur. The man who builds a 
6-inch telescope and sets it up in his back garden can hardly 
hope to photograph a star-field or a nebula as effectively as an 
observer using the Palomar 200-inch; nor can he measure the 
surface temperature of Mars or study the radio waves coming 
from outer space. But this does not mean that he cannot make 
himself useful. Professional astronomers, with their great 
telescopes and complex equipment, have neither the time nor 
the inclination to make direct studies of objects which are 
comparatively near at hand. It is true that photographs are 
taken, but there are times when no photograph can equal sheer 
visual observations at the eye-end of a telescope. 

To drive home this point, it will be useful to give a definite 
instance of what I mean. In 1955, it was found that the planet 
Jupiter is a source of "radio waves", or radiation of very long 
wave-length. This discovery was most interesting, because until 
then it had been thought that all radio sources except the Sun 
lay in the depths of space, well beyond our own Solar System. 
Research workers wanted to find out whether the waves came 
from the planet as a whole, or whether they were emitted by a 
few definite features on the surface. They therefore appealed to 
the Jupiter Section of the British Astronomical Association, 
whose members had been making regular observations of the 
surface features and knew them extremely well. The B.A.A. 
amateurs suddenly found that their patient labours of past years 
had become of major importance. 

Any serious amateur can do valuable work by making 
systematic physical observations of the planets, searching for 
comets, and studying the fluctuations of variable stars. On the 
other hand, aimless and haphazard enthusiasm is of no use 
whatsoever. One has to be methodical, and normally any one 
observer will confine himself to a particular study, since he 
will not have time to cover the whole field. Some amateurs 
concentrate upon variable stars, and show marked annoyance 
when the Moon drowns faint objects with her light; others 
spend their astronomical time wholly upon lunar work, and 
never look at a star except to test their telescopes, while Mars, 
Jupiter and Saturn all have their followers. 

The favourite question asked by the non-enthusiast is: 
"What is the immediate use of astronomy? Why do people 



spend their time watching stars and planets millions of 
miles away, when there is so much to be done on our own 
world ?" 

On the face of it, the question is quite reasonable. It is not 
immediately obvious why an astronomer should become excited 
at the appearance of a spot on Saturn, or the flaring-up of a 
new star. But it must not be forgotten that astronomy is only 
one branch of science; it has strong links with chemistry, physics 
and optics, and the stars are vast natural laboratories in which 
research workers can study matter in unfamiliar states. It is 
interesting to remember that helium gas, second lightest of the 
elements, was first found in the Sun. Not until years later was 
it detected on Earth, and subsequently used to inflate the gas- 
bags of airships and balloons ; its identification was made easier 
by the fact that its existence was already known. 

All timekeeping and navigation is based on astronomy. 
Greenwich Observatory was originally founded, by order of 
Charles II, so that a new. star catalogue could be drawn up for 
the use of British seamen. In fact, astronomy is far from being 
the useless study that so many people imagine. One cannot 
separate it from other sciences any more than one can separate 
arithmetic from algebra. 

Yet there is another aspect to be considered. In this age of 
specialization, we are in danger of becoming too concerned 
with material benefit. What, for instance, is the actual use of 
a Van Gogh portrait or a Beethoven symphony? The only 
answer is that a great picture or a great piece of music can give 
enjoyment to millions of people. And the same is true of 
astronomy. No painting can equal the sight of the rings of 
Saturn or the countless stars of the Milky Way; Man can never 
surpass Nature in her own realm. 

Even those who are preoccupied with everyday affairs, 
and can spare little time for studying the skies, will find 
astronomy well worth while. If the mildly enthusiastic amateur 
has no ambition to build or buy a telescope large enough for 
him to do useful work, he can still give himself hours of pleasure 
by observing for his own amusement, and as he learns he will 
find the horizon opening out before him. What does it matter if 
he never discovers a comet or solves the riddle of the Martian 
clouds? Few people who learn the piano in their spare time 



have any delusions that they will end by playing as brilliantly 
as Paderewski, 

However, one cannot draw the best out of astronomy 
without taking some trouble. The night sky becomes far more 
attractive once the Great Bear, the Dragon and all the other 
constellations can be recognized on sight, while a planet grows 
in fascination as its true nature becomes known. The aim of 
my present book b to explain the basic facts as clearly and 
as simply as possible, as well as indicating some lines of work 
which can be undertaken by the amateur who wants to make 
himself useful to others. It is, in fact, an attempt to answer 
the second oft-asked question: "If I want to make a hobby of 
astronomy, how do I go about it ?" 


Chapter Two 


A subject can always be better understood if some- 
thing is known about its history. Though we no longer worship 
our "honourable ancestors", it is a distinct help to look back 
through time in order to see how knowledge has been built up 
through the centuries. This is particularly true with astro- 
nomy, which is the oldest science in the world — so old, indeed, 
that we do not know when it began. 

Most people of to-day have at least some knowledge of the 
universe in which we live. The Earth is a globe nearly 8,000 
inilcs in diameter, and is one of nine "planets" revolving 
round the Sun. The best way of describing the difference 
between a planet and a star is to say that the Earth is a typical 
planet, while the Sun is a typical star. 

Five planets — Mercury, Venus, Mars, Jupiter and Saturn — 
were known to the ancients, while three more have been dis- 
covered in modern times. Jupiter is the largest of them, and its 
vast globe could hold more than a thousand bodies the size of 
the Earth, but even Jupiter is tiny compared with the Sun, The 
stars of the night-sky are themselves suns, many of them far 
larger and more brilliant than our own, and appearing small 
and faint only because they are so far away. On the other hand, 
the Moon shines more brilliantly than any other body in our 
skies apart from the Sun. This importance is not real ; the Moon 
is a most insignificant body, and has no Ught of its own. It 
has a diameter only one-quarter of that of the Earth, and is by 
far the closest non-artificial object in the heavens. 

The whole celestial vault seems to revolve round the Earth 
once a day. This apparent motion is due, of course, to the fact 
that the Earth is spinning on its axis from west to east. Of all 
the natural bodies in the sky, only the Moon has a real move- 
ment round the Earth. 

We are used to taking these facts for granted, but at the start 
of human history it was believed that the Earth was flat and 
stationary. The Sun and Moon were worshipped as gods, while 

b 17 


the appearance of something unusual in the heavens was taken 
as a sign of divine displeasure. 

It is usually said that the Erst astronomers were the Chald- 
eans, the Egyptians and the Chinese, but this is only partially 
correct. It is true that these ancient folk divided the fixed 
stars into groups or "constellations", and also recorded 
planets, comets and eclipses, but they had no real understand- 
ing of the nature of the universe or even of the Earth itself, 
so that they were hardly "astronomers" in the full sense of the 

The story begins in about 3000 B.C., when the 365-day 
year was first adopted in Egypt and in China. This, too, was 
the approximate date of the building of that remarkable 
structure known as the Great Pyramid of Cheops. The Pyramid 
is^ still one of the main tourist attractions of Egypt; Cheops 
himself, a harsh and determined ruler, spent so much money 
upon it that he ruined his country, and even now we are not 
certain why he regarded the Pyramid as so important. From an 
astronomical point of view, it is interesting because its main 
passage is oriented with the north pole of the sky. 

The Earth's axis of rotation 

♦ is inclined at an angle of 23^ 

. oons degrees, and points northwards 

to the celestial pole (Fig. 1). 

To-day the pole is marked 

approximately by a bright star 

known as Polaris, familiar to 

/ every navigator because it 

/ seems to remain almost station- 

- — ./NORTH ary whi ] e ^ other cc i est j a] 

f \ POLE bodies revolve round it. In 

I j Cheops' time, however, the 

SOUTH V ^ / polar point was in a different 

POLE r~ position, close to a much fainter 

/ star, Thuban, in the constella- 

tion of the Dragon. The reason 
Fig. 1. The axis of the Earth. f °r this change is that the Earth 

is "wobbling" slightly, like a 
top that is about to fall, and the direction of the axis is describ- 
ing a circle in the sky. The wobbling is very slow, but the shift 



of the pole has become appreciable since the Pyramid was built 
5,000 years ago. 

Egypt is still regarded as the land of mystery. As a matter 
of fact, most of the mysteries of Ancient Egypt were deliberately 
created by the priests, who were the most learned of their race 
and who realized that the best way of controlling the common 
people was to keep them in ignorance. Even the priests had 
marked limitations, and although they excelled in the art of 
making exact measurements, and in land survey, they never 
found out that the Earth is a globe. They believed the world to 
be rectangular, with Egypt in the middle and deserts and seas 
all round. 

Chinese astronomy was no more advanced. Records of 
comets and eclipses have come down to us, but some of the 
ideas held in those times seem strange to-day. One famous 
story about an eclipse will show what is meant. 

The Moon revolves round the Earth once a month, while the 
Earth revolves round the Sun once a year. The Moon is much 
smaller than the Sun, but it is also much closer, so that in our 
skies the two look almost exactly the same size. When the Sun, 
Moon and Earth move into a straight line, with the Moon 
in the middle, we see what is known as a solar eclipse; the dark, 
non-luminous body of the Moon blots out the Sun, and for a 
few minutes "day is turned into night". If the Moon covers the 
Sun completely, the eclipse is total. 

The Chinese knew about eclipses, and even worked out how 
to predict them, but they had no idea that the Moon was respon- 
sible. They thought that the Sun was in danger of being 
swallowed by a hungry dragon, and they therefore made it 
their custom to beat gonp and pans as loudly as possible, 
hoping that the noise would scare the dragon away. (It always 
did!) In 2136 B.C. the Court Astronomers, Hsi and Ho, failed 
to give warning that an eclipse was due, and in consequence no 
preparations could be made. The luckless two were held to have 
imperilled the whole world by their neglect of duty, and were 
executed. The story may or may not be true! 

Astronomy in its true form began with the Greeks, who not 
only made observations but who also tried to explain them. The 
first of the great philosophers was Thales of Miletus, who was 
born in 624 B.C.; the last was Ptolemy of Alexandria, and with 



his death, in or about a.d. 180, the classical period of science 
comes to an end. During the intervening eight centuries, 
human thought made remarkable progress. 

Thales himself may have been the first to realize that the 
Earth is a globe, but unfortunately all his original writings have 
been lost. The first definite arguments against the old idea of a 
flat Earth were given by Aristotle, who was born in 384 B.C. 
and died in 322. Aristotle was one of the most brilliant men of 
the ancient world, and his reasoning shows the Greek mind at 
its best. 

As Aristotle points out, the stars appear to alter in altitude 
above the horizon according to the latitude of the observer. 
Polaris appears to remain fairly high in the sky as seen from 
Greece, because Greece is well north of the terrestrial equator; 
from Egypt, Polaris is lower; from southern latitudes it cannot 
be seen at all, since it never rises above the horizon. On the 
other hand Canopus, a brilliant star in the southern part of 
the sky, can be seen from Egypt but not from Greece. This is 
just what would be expected on the theory of a round Earth, 
but such behaviour cannot possibly be explained if we suppose 
the Earth to be flat. Aristotle also noticed that during a lunar 
eclipse, when the Earth's shadow falls across the Moon, the 
edge of the shadow appears curved— indicating that the surface 
of the Earth must also be curved. 

The next step was taken by 
Eratosthenes of Gyrene, who 
succeeded in measuring the 
length of the Earth's circum- 
ference. His method was most 
ingenious, and proved to be 
remarkably accurate. Eratos- 
thenes was in charge of a great 
scientific library at Alexandria, 
in Egypt, and from one of the 
books available to him he 
learned that at the time of the 

summer solstice, the "longest 

Fjg. 2. Eratosthenes' method of ,*-„» :„ „ „,-.!,„ ' 1 „*,■., ■ S T. 

measuring the circumference of J ay DOrtIlern latitudes, the 

the Earth. Sun was vertically overhead at 

noon as seen from the town of 



Syene (the modern Assouan), some distance up the Nile. At 
Alexandria, however, the Sun was at this moment 7 degrees 
away from the overhead point, as is shown in Fig. 2. A full circle 
contains 360 degrees, and 7 is about 1 /50 of 360, so that if the 
Earth is spherical its circumference must be 50 times the distance 
from Alexandria to Syene. Eratosthenes may have arrived 
at the final figure of 24,850 miles, which is only fifty miles too 

If the Greeks had taken one step more, and placed the 
Sun in the centre of the planetary system, the progress of 
astronomy would have been rapid. Some of the philosophers 
tried to do so; but unfortunately Aristotle held the Earth to be 
the centre of the universe, and Aristotle's authority was so great 
that few people dared to question it. Moreover, the decentral- 
ization of the Earth would have meant a change in the laws of 
"physics", since Aristotle's idea of "things seeking their 
natural place" would have been much disturbed. 

Most of our knowledge of Greek astronomy is due to Claudius 
Ptolema^us (Ptolemy), who wrote a great book known gener- 
ally by its Arab title of the Almagest. In it, he sums up the ideas 
of the great philosophers who had lived before him; and the 
theory that the Earth lies at rest in the centre of the universe 
is therefore called the "Ptolemaic", though as a matter of fact 
Ptolemy himself was not directiy responsible for it. 

On the Ptolemaic theory, all the celestial bodies move round 
the Earth. Closest to us is the Moon; then come Mercury, 
Venus, the Sun, Mars, Jupiter, Saturn and finally the stars. 
Ptolemy maintained that since the circle is the "perfect" form, 
and nothing short of perfection can be allowed in the heavens 
all these bodies must move in circular paths. Unfortunately, 
the planets have their own ways of behaving. Ptolemy was an 
excellent mathematician, and he knew quite well that the 
planetary motions cannot be explained on the hypothesis of 
uniform circular motion round a central Earth. He therefore 
worked out a complex system according to which each planet 
moved in a small circle or "epicycle", the centre of which itself 
moved round the Earth in a perfect circle. As more and more 
irregularities came to light, more and more epicycles had to be 

There is some doubt as to whether Eratosthenes' estimate was accurate to 
within a few tens of miles, but at least his results were not wildly in error, 



introduced, until the whole system became hopelessly artificial 
and cumbersome. 

Hipparchus, who had lived some two centuries before 
Ptolemy, had drawn up a detailed and accurate star catalogue. 
The original has been lost, but fortunately Ptolemy reproduced 
it in his Almagest, so that most of the work has come down to 
us. Hipparchus was also the inventor of an entirely new branch 
of mathematics, known to us as trigonometry. 

When the power of Greece crumbled away, astronomical 
progress came to an abrupt halt. The great library at Alexandria 
was looted and burned in a.d. 640, by order of the Arab caliph 
Omar, though in fact most of the books may have been scattered 
earlier; in any case, the loss of the Library books was irreparable, 
and scholars have never ceased to regret it. For several centuries 
very little was done. When interest in the skies did return, it 
came— ironically enough— by way of astrology. 

Even to-day, there are still some people who do not know the 
difference between astrology and astronomy. Actually, the 
two are utterly different. Astronomy is an exact science; as- 
trology is a relic of the past, and there is no scientific basis for 
it, though in some countries (notably India) It still has a con- 
siderable following. 

The best way to define astrology is to say that it is the 
superstition of the stars. Each celestial body is supposed to 
have a definite influence upon the character and destiny of 
each human being, and by casting a horoscope, which is 
basically a chart of the positions of the planets at the time of the 
subject's birth, an astrologer claims to be able to foretell the 
destiny of the person for whom the horoscope is cast. There 
may have been some excuse for this sort of thing in the Dark 
Ages, but there is none to-day. The best that can be said of 
astrology is that it is fairly harmless so long as it is confined 
to circus tents and the less serious columns of the Sunday 

However, mediaeval astrology did at least lead to a revival of 
true astronomy. The Arabs led the way, and presently interest 
spread to Europe. Star catalogues were improved, and the 
movements of the Moon and planets were re-examined. There 
were even observatories; very different from the domed 
buildings of to-day, but observatories none the less. 



Astronomy was still crippled by the blind faith in Ptolemy's 
system. So long as men refused to believe that the Earth could 
be in motion, no real progress could be made. The situation was 
not improved by the attitude of the Church, which in those 
times was all-powerful. Any criticism of Aristotle was regarded 
as heresy. Since the usual fate of a heretic was to be burned at 
the stake, it was clearly unwise to be too candid. 

The first serious signs of the approaching struggle came in 
1 546, with the publication of De Revoluttombw Orbitim Ccelestium 
(Concerning the Revolutions of the Heavenly Bodies) by a Polish 
canon, Nicolas Copernicus. Copernicus was a clear tlunker, as 
well as being a skilful mathematician, and at a fairly early 
stage in his career he saw so many weak links in the Ptolemaic 
system that he felt bound to abandon it. It seemed unreason- 
able to suppose that the stars could circle the Earth once a day. 
In his own words, "Why should we hesitate to grant the Earth 
a motion natural and corresponding to its spherical form ? And 
why are we not willing to acknowledge that the appearance of a 
daily rotation belongs to the heavens, its actuality to the Earth ? 
The relation is similar to that of which Virgil's ^Eneas said, 
'We sail out of the harbour, and the countries and cities 
recede.' " 

Copernicus' next step was even bolder. He saw that the 
movements of the Sun, Moon and planets could not be ex- 
plained by the old system even when all Ptolemy's circles and 
epicycles had been allowed for, and so he rejected the whole 
theory. He placed the Sun in the centre of the system, and 
reduced the status of the Earth to that of a perfectly ordinary 

Copernicus was wise enough to be cautious. He knew that 
he was certain to be accused of heresy, and though his book 
was probably complete by 1530 he refused to publish it until 
the year of his death. As he had foreseen, the Church was 
openly hostile. Bitter arguments raged throughout the next 
half-century, and one philosopher, Giordano Bruno, was 
burned in Rome because he insisted that Copernicus had 
been right.* 

Tycho Brahe, born in Denmark only a few months after 

* This was noi Bruno's only crime in the eyes of the Church, but it was certainly 
a serious one. 



Copernicus died, was utterly unlike the gentle, learned Polish 
mathematician. Tycho was a firm believer in astrology, and an 
equally firm disbeliever in the Copernjcan system, so that it 
is ironical to realize that his own work did much to prove the 
truth of the new ideas. He built an observatory on the island 
of Hven, in the Baltic, and between 1576 and 1596 he made 
thousands of very accurate observations of the positions of the 
stars and planets, finally producing a catalogue that was far 
better than Ptolemy's. Of course, he had no telescopes; 
but his measuring instruments were the best of their time, and 
Tycho himself was a magnificent observer. 

The story of his life would need a complete book to itself. 
Tycho is, indeed, one of the most fascinating characters in the 
history of astronomy. He was proud, imperious and grasping, 
with a wonderful sense of his own importance; he was also 
landlord of Hven, and the islanders had little cause to love him. 
His observatory was even equipped with a prison, while his 
retinue is said to have included a pet dwarf. Yet despite all his 
shortcomings, he must rank with the intellectual giants of 
his age. Nowadays, nothing remains of his great Uraniborg 

When Tycho died, in 160 1, he left his observations to Ms 
assistant, a young German mathematician named Johann 
Kepler. After years of careful study, Kepler saw that the 
movements of the planets could be explained neither by 
circular motion round the Earth, nor by circular motion round 
the Sun, so that there was something wrong with Copernicus' 
system as well as with that of Ptolemy. Finally, he found the 

answer. The planets do 
indeed revolve round the 
Sun, but not in perfect 
circles. Their paths, or 
\ "orbits", are elliptical. 
) One way to draw an 
ellipse is shown in Fig. 3. 
Fix two pins in a board 

* 3. Me.od of tawi „ E ancllip « e . tJXX^A 
amount of slack. Now loop a pencil to the thread, and draw it 
round the pins, keeping the thread tight. The result will be an 

2 4 


ellipse,* and the distance between the two pins or "foci" 
will be a measure of the eccentricity of the ellipse. If the foci 
are close together, the eccentricity will be small, and the 
ellipse very little different from a circle ; if the foci are widely 
separated, the ellipse will be long and narrow. 

The five planets known in Kepler's day proved to have 
paths which were almost circular, but not quite. The slight 
departure from perfect circularity made all the difference, 
and Tycho's observations fell beautifully into place, like the 
last pieces of a jig-saw puzzle. The age-old problem had been 
solved, though the Church authorities continued to oppose the 
truth for some time longer. Kepler's three Laws of Planetary 
Motion, the last of which was published in 1618, paved the 
way for the later work of Sir Isaac Newton. 

Kepler's work was not the only important development to 
enrich the early part of the seventeenth century. In 1608 a 
spectacle-maker of Middelburg in Holland, Hans Lippersheim, 
found that by arranging two lenses in a particular way he 
could obtain magnified views of distant objects. Spectacles 
had been in use for some time— according to some authorities, 
they were invented by Roger Bacon— but nobody had hit upon 
the principle of the telescope until Lippersheim did so, more 
or less by accident. 



Fig. 4. Principle of the refractor. 

A refracting telescope consists basically of two lenses. One, 
the larger, is the object-glass ; its function is to collect the rays 
of light coming from a distant object, and bunch them together 
to form an image at the focus (Fig. 4}. The image is then 
magnified by a smaller lens known as an eye-piece. This is 
more or less the principle used in the naval and hand telescopes 
of to-day, as well as in ordinary binoculars. 

* The method a excellent in theory. In practice, what usually happens is that 
the pins fall down or the thread breaks. One day, I hope to carry out the whole 
manoeuvre successfully. 



The news of the discovery spread across Europe, and came to 
the ears of Galileo Galilei, Professor of Mathematics at the 
University of Padua. Galileo was quick to see that the telescope 
could be put to astronomical use, and "sparing neither trouble 
nor expense", as he himself wrote, he built an instrument of his 
own. It was a tiny thing, pitifully feeble compared with a 
modern pocket telescope, but it helped towards a complete 
revolution in scientific thought. 

Galileo's first telescopic views of the heavens were obtained 
towards the end of 1609. At once, the universe began to unfold 
before his eyes. The Moon was covered with dark plains, lofty 
mountains and giant craters; Venus, the Evening Star of the 
ancients, presented lunar-type phases, to that it was sometimes 
crescent, sometimes half and sometimes nearly full ; Jupiter was 
attended by four moons of its own, while the Milky Way proved 
to be made up of innumerable faint stars. 

Galileo had always believed in the new system of the 
universe, and his telescopic work made him even more certain. 
Inevitably he found himself in trouble with the Church. It 
was hard for religious leaders to realize that the Earth is not 
the most important body in the universe, and Galileo seemed 
to them to be a dangerous heretic. He was arrested and im- 
prisoned, after which he was brought to trial and forced to 
"curse and abjure and detest" the false theory that the Earth 
moves round the Sun. 

Few people were deceived, and before the end of the century 
the Ptolemaic theory had been abandoned for ever. The 
publication of Isaac Newton's Prindpia, in 1687, led to a real 
understanding of the way in which the planets move. 

Most people have heard the story of Newton and the apple. 
It is interesting because unlike most stories of similar type, 
such as Canute and the waves, it is probably true. Apparently 
Newton was sitting in his garden one day when he saw an apple 
fall from its branch to the ground, and upon reflection he 
realized that the force pulling on the apple was the same force 
as that which keeps the Moon in its path round the Earth. From 
this he was led on to the idea of "gravitation", upon which the 
whole of later research has been based. It is fair to say that 
Kepler found out "how" the planets move; Newton discovered 
"why" they do so. 



Newton also constructed an entirely new type of telescope. 
As has been shown, Galileo's instrument was a refractor, 
and used an object-glass to collect its light. Newton came to 
the conclusion that refractors would never be really satis- 
factory, and he looked for some way out of the difficulty. 
Finally he decided to do away with object-glasses altogether, 
and to collect the light by means of a specially-shaped mirror. 

When Newton rejected the refractor as unsatisfactory, he 
was making one of his rare mistakes. However, the Newtonian 
"reflector" soon became popular, and has remained so. 
Mirrors are easier to build than lenses, and even to-day all the 
world's largest instruments are of the reflecting type. 

Astronomy was growing up. So long as observations had to 
be made with the naked eye alone, little could be learned about 
the nature of the planets and stars ; their movements could be 
studied, but that was all. As soon as telescopes became available, 
true observatories made their appearance. Copenhagen and 
Leyden took the lead ; the Paris Observatory was completed in 
1671, and Greenwich in 1675. 

Greenwich was founded for a special reason. England has 
always been a seafaring nation, and before the development of 
reliable clocks the only way in which sailors could fix their 
position when far out in the ocean, out of sight of land, was to 
observe the position of the Moon among the stars. This involved 
the use of a good star catalogue, and the best one available, 
Tycho's, was still not accurate enough. Charles II therefore 
ordered that the star places must be "anew observed, examined 
and corrected for the use of my seamen". A site was selected in 
the Royal Park at Greenwich, and Sir Christopher Wren, 
himself a former professor of astronomy, designed the first 
observatory building. The Rev. John Flamsteed was appointed 
Astronomer Royal, and in due course the revised star catalogue 
was completed. 

Telescopes continued to be improved. Some of the early 
instruments were curious indeed; one of them, used by the 
Dutch observer Christiaan Huygens, was over 200 feet long, 
so that the object-glass had to be fixed to a mast. But gradually 
the worst difficulties were overcome, and both refractors and 
reflectors gained in power and in convenience. Mathematical 
astronomy made equally rapid strides. The great obstacle had 



always been the Ptolemaic system, and once that had been 
swept away the path was clear. The distance between the Earth 
and the Sun was measured with fair accuracy, and in 1675 
the Danish astronomer Ole Earner even measured the speed 
of light, which proved to be 186,000 miles per second. Romer 
did this, incidentally, by observing the movements of the 
four bright moons of Jupiter. 

But though knowledge of the bodies of the Solar System had 
improved out of all recognition, little was known about the stars, 
which were still regarded as mere points of reference. The first 
serious attack on their problems was made by William Herschel, 
who is righdy termed the "father of stellar astronomy". 

Herschel was born in Hanover in 1738, eleven years after 
the death of Newton. He came to England, and became 
organist at the Octagon Chapel in Bath; but bis main interest 
was astronomy, and he built reflecting telescopes which were 
the best of their age. The largest of Herschel's telescopes, com- 
pleted in 1789, had a mirror 48 inches in diameter and a focal 
length of 40 feet. The mirror still exists, and now hangs on the 
wall of Flamsteed House in Greenwich, though it has not been 
used since Herschel's time. 

Herschel had his living to earn, and for some years he could 
not afford to spend all his time in studying astronomy. Then, 
in 1781, he made a discovery which altered his whole life. 
One night he was examining some faint stars in the constella- 
tion of the Twins, when he came across an object which was 
certainly not a star. At first he took it for a comet, but as soon 
as its path was worked out there could no longer be any doubt 
as to its nature. It was not a comet, but a planet— the world we 
now call Uranus, 

The discovery was quite unexpected. There were five known 
planets, and these, together with the Sun and Moon, made a 
grand total of seven. Seven was the magical number of the 
ancients, and it had therefore been thought that the Solar 
System must be complete. Herschel became world-famous; 
he was appointed Court Astronomer to King George HI, and 
henceforth he was able to give up his musical career altogether, 

Herschel set himself a tremendous programme. He decided 
to explore the whole heavens, so that he could form some idea 
of the way in which the stars were arranged. Until the end of his 



long life, in 1822, he worked patiently at his task, and his final 
conclusions have been proved to be reasonably accurate. 

Naturally, Herschel made numerous discoveries during his 
sky-sweeps. Many apparently single stars proved to be double, 
and there were also clusters of stars, as well as faint luminous 
patches known as "nebuhe", from the Latin word meaning 
"clouds'*. Herschel was a most pai n staking observer. He 
catalogued all his discoveries, and when we examine his pub- 
lished papers we can only marvel at the amount of work he 
managed to do. Since he lived in England for most of his life, 
he was unable to examine the stars of the far south, which 
never rise in northern latitudes, and it was fitting that the 
completion of his sky-sweeps should be accomplished later by 
his son, Sir John Herschel, who travelled to the Cape of Good 
Hope specially for the purpose, and remained there for several 

Another famous observer of this period was Johann Schroter, 
chief magistrate of the little German town of Lilienthal. Unlike 
Herschel, Schroter concentrated mainly upon the Moon and 
planets, and he is the real founder of "selenography", the 
physical study of the lunar surface. Unfortunately Schroter's 
observatory, together with all his unpublished work, was 
destroyed by the invading French armies in 1814, and Schroter 
himself died two years later. 

In the early years of the nineteenth century a German 
optician, Fraunhofer, began to experiment with glass prisms. 
Newton had already found that ordinary "white" light is not 
white at all, but is a blend of all the colours of the rainbow. 
Fraunhofer realized that this discovery could be turned to 
good account, and his work led to the development of a new 
instrument, the astronomical spectroscope. 

Just as a telescope collects light, so a spectroscope analyses 
it. By studying the "spectra" produced, it is possible to find 
out a great deal about the matter present in the material which 
is emitting the light. For instance, the spectrum of the Sun 
shows two dark lines which can be due only to the element 
sodium, so that we can prove that sodium exists in the Sun. 

Spectroscopes can be made by amateurs, but we have to 
admit that little useful work can be done except with complex 
and expensive equipment. To the professional astronomer of 



to-day, the telescope would be of little use without the spec- 
troscope; it is now possible to track down familiar elements in 
remote stars, and even in other star-systems far away in the 
depths of space. 

In 1838, Friedrich Besscl, Director of the Observatory of 
Konigsberg, returned to the problem of the distances of the 
stars. By studying the apparent movements of 61 Cygni, a faint 
object in the constellation of the Swan, he was able to show that 
it lay at a distance of about 60 million million miles. About the 
same time a British astronomer, Henderson, measured the 
distance of the bright southern star Alpha Gentauri, and 
arrived at the reasonably accurate value of twenty million 
million miles; the real value is about 24 million million miles, 
so that Henderson underestimated somewhat. Alpha Gentauri is 
a triple star, and the faintest member of the trio remains the 
nearest known body outside our own Solar System. 

Twenty-four million million miles ! Our brains are not built 
to understand such vast distances, and it is clear that the 
mile is too short to be a convenient unit of length. One might 
as well try to measure the distance between London and 
Melbourne in centimetres. Fortunately there is a much better 
unit available, based upon the speed of light. 

Light is known to travel at 186,000 miles per second. A ray 
from the Sun takes 8$ minutes to reach us, but in the case of 
Alpha Gentauri the time of travel is 4J years; we see the star 
not as it is now, but as it was 4! years ago. Alpha Gentauri is 
therefore said to be 4J light-years away, while the distance of 
61 Cygni is nearly 1 1 light-years. 

Bessel's success gives us an added idea of the real unimport- 
ance of the Solar System. Rather than quote strings of figures, 
it will be more graphic to imagine a scale model. If we begin 
with making the Sun a 2-foot globe, and putting it on West- 
minster Bridge, the Earth will become a pea at a distance 01 
215 feet; Uranus, the outermost of the planets known in 
Bessel's time, will be represented by a plum £ of a mile away 
from our 2-foot Sun. What of the nearest star? We shall not find 
it in London, or even in England; it will lie some 10,000 miles 
away, in the frozen wastes of Siberia. We have learned much 
since the days when the Earth was thought to be the hub of 
the universe. 



Another great event of the last century was the beginning of 
astronomical photography. In 1845 ^ c nrst "Daguerreotype" 
picture of the Sun was taken, followed in 1850 by a good 
photograph of the Moon. Within fifty years, magnificent photo- 
graphs of the celestial bodies were being taken not only at the 
official observatories, but also by amateurs. To-day most of the 
regular work of the professional astronomer is done with the aid 
of photography, and sheer visual observation is rare, since in 
general the photograph is not only more reliable than the eye 
but also leaves a permanent record. It can also detect objects 
too faint to be seen by visual means. 

Herschel' s 48-inch reflector was soon surpassed. In 1845 
Lord Rosse, in Ireland, built a 72-inch. It was cumbersome and 
awkward to use, but it was by far the most powerful instrument 
then in existence, and Rosse used it to study the clusters and 
nebula: which had been pointed out by Herschel. Some of the 
ncbulse proved to consist entirely of faint stars, though others 
could not be so resolved. Even more interesting was the fact that 
some of the starry nebulae revealed a spiral structure, so that 
they looked very much like Catherine-wheels. 

Alone, the telescope could never decide upon the nature of 
the irresolvable nebula;; the spectroscope was able to do so. 
In 1864 Sir William Huggins examined a faint nebula in the 
Dragon, and found that it was made up not of stars, but of 
luminous gas. 

It is now known that the nebular objects are of three types. 
Inside our own star-system, known commonly as the Milky 
Way but more properly as the Galaxy, we find the normal star- 
clusters and the gaseous nebulae, most of them hundreds or 
thousands of light-years from us. Beyond the Galaxy there is a 
vast gulf, and then we come to the separate external systems, 
lying at immense distances. The most famous of them is the 
Great Spiral in Andromeda, which can be seen with the naked 
eye as a faint misty patch, and which proves to be a galaxy in its 
own right, even larger than our own. Herschel had suspected 
something of the sort, and the work of Rosse and Huggins 
supported his view, though the question was not finally settled 
until 1923. 

Even the Rosse 72-inch did not retain its lead for long. 
Each decade saw the arrival of newer and larger telescopes. In 



1 91 7 came the 100-inch reflector at Mount Wilson, which 
remained the greatest in the world until 1948, when it was sur- 
passed by the 200-inch at Palomar, 

At present (1978) the world's largest telescope is the 236- 
inch Russian reflector, which has been set up in Siberia; no 
positive results have been obtained from it as yet, but no doubt 
it will play a major role in the years to come. Yet the main 
need today is not for larger and larger telescopes, but for more 
reflectors of the too to 150-inch aperture range. Many of these 
are now being set up in the southern hemisphere, where they 
can be used to best advantage; for instance there is the 140-inch 
at Siding Spring in Australia, as well as 150- and 158-inch 
instruments in Chile. 

During the past few decades there have been remarkable 
developments in other branches of astronomy. The first dates 
from the early 1930*3, when an engineer named Karl Jansky, 
working for the Bell Telephone Company, was investigating 
problems of "static" and found that he was picking up radio 
waves from the sky. This was the beginning of radio astronomy, 
which has now come so very much to the fore. 

Radio telescopes are not in the least like optical telescopes, 
and they do not produce visible pictures of the objects under 
study; one cannot look through them, as some earnest inquirers 
fondly believe! They are designed to collect the long- wavelength 
radiations coming from space, and they arc of many different 
designs. The most famous radio telescope is probably the 250- 
foot steerable "dish" at Jodrell Bank, in England, but each 
design is tailored to suit its own special needs, I am not a radio 
astronomer, but electronically-minded amateurs will certainly 
find plenty of scope. Grote Reber, who built a "dish" before 
the war and was probably the first true radio astronomer, was 
an amateur. 

Associated with radio astronomy is radar astronomy, which 
involves the transmission of pulses of energy, which are 
"bounced back" off remote bodies; the echo is picked up, and 
valuable information gained. It is in this way, by bouncing radar 
pulses off the planet Venus, that we have obtained the best 
value for the astronomical unit, or Earth-Sun distance. But 
radar astronomy is not an amateur pursuit, and I do not propose 
to follow it up here. 



Advances in what may be termed "pure astronomy" have 
been spectacular. For instance, entirely new kinds of objects 
have been discovered during the past decades: there are the 
remote, super-luminous "quasars", whose nature is still very 
uncertain, and the almost equally strange, rapidly-varying 
radio sources which we call "pulsars". In addition, we have 
entered the Space Age, and there is no longer any sharp boun- 
dary between the ancient science of astronomy and the new 
science of astronautics. 

The new era opened on October 4, 1957, when the Russians 
sent up the first artificial satellite, Sputnik I. The first man in 
space, the late Yuri Gagarin, made his pioneer flight in 1961 ; 
subsequently, unmanned probes were sent to the planets Venus 
and Mars, and close-range photographs were taken of the 
crater-scarred surface of die Moon. As the years raced by, it 
became very clear that space-travel was approaching. And as 
everyone knows, the Moon was reached in July 1969, when 
Neil Armstrong and Edwin Aldrin stepped out on to the bleak 
lunar rocks. 

All this has caused a revolution in outlook, and it has been 
claimed that the day of the amateur astronomer is over. This is 
something which I would dispute most vehemendy. It is quite 
true that his field of research is more limited than it used to be; 
but his role remains as important as ever. He has to become 
more specialized, but there is no falUng-off in the value of his 

I am writing these words in early 1978. Before they appear in 
print, much may have happened, but the basic problems wfiJ 
remain unaltered. And as one puzzle is solved, a host of others 
arises to take its place. This has been the case since ancient 
times; it is still the case today. 


Chapter Three 


The casual sky- watcher will be able to give himself 
hours of enjoyment with the help of nothing more than a pair 
of binoculars. If he takes the trouble to learn the patterns of 
the constellations, he will be able to find dozens of double 
tbm, coloured stars, clusters and nebula, and he will have no 
difficulty in tracing the slow movements of the planets against 
their starry background. Some branches of work, such as the 
recording of Polar Lights, can be done without any equipment 

3-t 3,1 J. 

On the other hand, most of those who feel really drawn 
towards astronomy will want to obtain some kind of a telescope. 
No drawing or photograph can give any real idea of the beauty 
of the lunar mountains, the rings of Saturn, or the myriads of 
stars in a rich cluster, any more than a rough copy can convey 
the power and beauty of the Mona Lisa. 

A few observatories, such as those at Preston, have "open 
nights", when members of the general public are allowed to 
go and look through a powerful telescope. This is admirable 
but there is always a queue, and the best that can be done is 
to have a quick glimpse at some famous object such as a star- 
cluster or a planet. Large instruments are always busy upon 
definite programmes, and normally they cannot be made 
available to amateurs; it would be unreasonable to expect any- 
thing of the sort, particularly as a hurried observation is worse 
than useless. Therefore, the beginner who wants to undertake 
telescopic work has to obtain equipment of his own. So far as 
choice is concerned, everything depends upon the interests and 
the financial resources of the observer. Let us make clear, at 
the outset, that proper astronomical telescopes are not cheap 
Moreoever, very small telescopes are of little value for real 
work— some that I have seen are less effective than good 

The beginner has the choice of depending upon binoculars, 



or making or buying a telescope. The equipment to be selected 
must depend upon the interests and the financial resources of 
the user. 

The refracting telescope, basically similar to the tiny 
instrument made by Galileo, is the usual form. The rays of 
light coining from the object under observation are collected 
by a lens or object-glass, which bunches the rays together and 
brings them to focus. The image produced is then enlarged by 
another lens, known as the eyepiece. All the actual magnifica- 
tion is done by the eyepiece, and various eyepieces can be 
fitted to the same telescope. 

This seems simple enough, but there are complications. 
For instance, the eyepiece is generally not a single lens, but a 
group of lenses held in a casing. The final view will be upside- 
down, unless deliberately corrected, but this does not matter in 
the least; in most astronomical photographs and drawings the 
south is at the top of the picture, with west to the left. 

Even the object-glass is not a single lens, and the reason for 
this is rather interesting. As Newton discovered, what we call 
"white" light is made up of all the colours of the rainbow, from 
red to violet. Light may be considered as a wave motion, and 
the distance from one crest 
to the next is called the 
wave-length (Fig. 5). Red 
light has a longer wave- 
length than blue or violet, -. ,., , _ . 

? , . . „ * Fig. "i. Wave-length. 

and the result is that the 6 J * 

object-glass does not bend it so much. The difference in the 
amount of bending or "refraction" means that the red rays 
are brought to focus at a greater distance from the object- 
glass (Fig. 6). This causes trouble, and the image of a bright 
object will appear to be surrounded by false colour. 

Newton failed to find the remedy, and it was for this reason 
that he abandoned refractors altogether. Actually, there is at 
least a partial answer. Modern object-glasses are made up of 
several lenses, composed of different kinds of glass whose 
chromatic properties tend to lessen the trouble. The effect can 
never be eliminated, but it can be very much reduced. 

A refractor is classified by the diameter of its object-glass. 
A "3-inch" has an object-glass 3 inches across, and so on. The 



largest refractor in the world, that of the Yerkes Observatory, 
is a 40-inch. 

^ The distance between a lens and its focal point is known as its 
"focal length", and this length divided by the diameter of the 
object-glass gives the "focal ratio" (usually abbreviated to 
"f/ratio"). For instance, I have a 3-inch refractor with a focal 
length of 36 inches. The f/ratio is therefore 36-7-3, or 12. The 
eyepiece combination has its own focal length, and the magni- 
fication obtained depends on the ratio of the focal length of the 

Fig. 6. Unequal refraction. The difference be- 
tween the refraction of red and violet light has 
been very much exaggerated, for the sake of 

eyepiece to that of the object-glass. In the case of my own 
f/12 refractor, an eyepiece of focal length f inch will give a 
magnification of 36 -r-^, or 72 diameters— usually written for 
short, as " x 72". With an object-glass of focal length 48 inches, 
the same eyepiece would give a power of 48 -i- £, or 96. 

It might therefore be thought that the way to get the best 
out of an eyepiece would be to use it with an object-glass of 
long focal length. Unfortunately this introduces other troubles, 
and the only solution is to strike a happy mean. 

Naturally, a large object-glass will collect more light than a 
smaller one. Suppose that I use a very short-focus eyepiece, say 
& inch, upon my 3-inch refractor? The magnification will be 
36 ---^, or 720. Yet the image will be so faint that nothing 
will be made out. The small object-glass, only 3 inches across, 
is quite unable to collect enough light to satisfy so powerful an 
eyepiece. If I want to use a magnification of 720, I must buy 
a larger telescope. 



Lens-making can be carried out only by a professional 
worker, and if the amateur wants to possess a refracting tele- 
scope of any size he has no alternative but to buy it. This 
is not the case with the reflector, and anyone with patience 
and a certain amount of manual skill can make himself a very 
adequate instrument. 

Newton's arrangement is shown in Fig. 7. Here the light 
from the distant object passes straight down an open tube until 
it strikes a mirror at the bottom. This mirror is shaped so as 
to reflect the rays back up the tube, directing them on to a 
smaller mirror called a flat. The flat is placed at an angle, 



t ' 

Rays of Light 



Fig. 7. Principle of the Newtonian reflector. For the sake 

of clarity, the curve of the main mirror has been much 


and sends the rays to the side of the tube, where they are 
brought to focus and are magnified by an eyepiece in the 
ordinary way. With a Newtonian reflector, therefore, the 
observer looks into the side of the tube instead of up it. Of 
course, the flat prevents some of the light-rays from reaching the 
main mirror at all, but the loss is not serious, and in any case 
there is no way of avoiding it. 

There is one great advantage in getting rid of the object- 
glass. A mirror reflects all colours equally, and so the trouble- 
some colour fringes do not appear. For this reason, colour 
estimates with a reflector are a good deal more reliable than 
those made with the help of a refractor, 

A reflector is classified according to the diameter of its main 
mirror. However, we must be careful when comparing mirrors 
with lenses; inch for inch, the lens will give a better result. 
A 6-inch refractor is appreciably more effective than a 6-inch 



reflector, so that it can be used with an eyepiece of higher 

Generally speaking, small and moderate reflectors have 
focal ratios of from f/7 to f/9. There are good reasons for this, 
but to enter into a full discussion would be beyond our present 
scope. Nor need we do more than mention the other types of 
reflecting telescopes; the Gregorian and the Cassegrain, in 
which the light is reflected back through a hole in the main 
mirror (Fig. 8), and the HerscheHan, in which the main 
mirror is tilted so as to dispense with the flat altogether (Fig. 
9). Gregorians and Herschelians have marked disadvantages, 
and the amateur will be wise to avoid them. The Cassegrain has 
many virtues, but on the whole the Newtonian is probably the 
best for amateur use. 





Rays of Light 

Fig. 8. Principle of the Cassegrain reflector. The "flat" is convex, 
and is just in front of the point of focus of the main mirror. In the 
Gregorian reflector, the "flat" is concave, and is placed just beyond 
the point of focus of the main mirror. The Gregorian gives an erect 



Rays of Light 


Fig. 9. Principle of the Herschelian reflector. This form of reflector 

is now virtually obsolete. 

Obviously, the performance of a reflector depends entirely 
upon its main mirror. The surface is coated with a layer of 
silver, aluminium or rhodium to make it highly reflective, but 




this is only part of the story. The shape of the curve must be 
extremely accurate, or the images produced will be distorted. 
The main mirror is consequendy the most expensive part of 
the whole instrument, if it is to be bought in a finished form. 

The principle of grinding a mirror into the correct optical 
curve is to use two disks of glass, at least an inch thick, one of 
which will turn into the final mirror while the other is merely a 
"tool". The tool is fastened to a bench, and the mirror placed on 
top of it, with water and carborundum powder between the 
two. The mirror is then slid to and fro, while the operator 
rotates it and also walla round the bench. Clearly, the tool will 
be worn away round the edge and will thus become convex, 
while the mirror will be worn away in the middle and will thus 
become concave (Fig. 10). 

This process is easy, and 
needs merely a good deal 
of patience until the curve 
is more or less correct. 
The mirror has then to be 
polished and figured, and 
a moment's carelessness 
will ruin hours of work. 
Numerous tests have to 
be made, and the real 
difficulty lies in the "figur- 
ing", which means pro- 
ducing the correct curve. 
But it can be done, and 
making a 6- or 8-inch 
mirror is within the capa- 
bilities of most people. I 

know of a fifteen-year-old enthusiast who has made himself a 
really good 6-inch reflector, and has also built the stand. A 
list of books giving full instructions will be found in the 
Appendix on page 344. 

The cost of the mirror and tool disks need not be more than 
£20, and the flat and eyepieces will swallow another £20, 
while the material for the tube and stand can be bought for a 
pound or so. In fact, £50 should cover the whole cost. The 
tube need not even be of rolled metal; it can be a skeleton of 


Fig. 10. Grinding a mirror. 


lattice construction with a square section, and the only rea 
requirement is that it should be firm. 

On the other hand, nobody should set out to grind a mirror 
without being prepared for a series of setbacks. Difficulties and 
problems arise at every turn, and there will be moments when 
the luckless operator feels inclined to hurl his mirror on to the 
ground and stamp on it. Patience is absolutely necessary — as 
is the case with almost everything in life. 

The construction of a mount is purely a mechanical task. 
One form, the altazimuth, is shown in Fig, n. Here the in- 
strument — in this case a 6-inch reflector— is resting in a cradle 
(A), and is kept in position solely by its own weight. The 
cradle can be rotated (B), and the telescope can be swung up 

or down by sliding the rod 
(C). The top of the rod is 
fitted with a worm (D), so 
that by moving the wheel the 
telescope can be moved very 
slightly up or down, while 
the handle (E), attached to a 
special form of joint, gives a 
similar slight rotation of the 
whole telescope. D and E are 
known as "slow motions". 
They are not essential, but 
they are certainly helpful. 

Fig, 12 shows a much sim- 
pler mount, this time for a 
3-inch refractor. It is simply 
a tripod, so that the tele- 
scope can be moved in any 
direction; slow motions are 
not always fitted, but cer- 
tainly make for easier observing. 

The next drawing, Fig. 13, is included as an Awful Warning. 
It is that appalling contrivance known as the Pillar and Claw 
Stand, beloved of dealers and despised by serious amateurs. 
It looks nice, and it is cheap, but it is about as steady as a 
blancmange. The slightest puff of wind will cause the whole 
telescope to quiver, and the object under observation will 


Fig. 1 1. Altazimuth mount, 
for a small reflector. 


appear to dance about like dice in a shaker. Anyone who 
buys a small refractor may well find that it is mounted upon 
a pillar and claw. If any real work is to be done, the only 
solution is to buy a rigid tripod and consign the original stand 
to the dustbin. 

Lastly, we come to the Equatorial Stand (Fig. 14), which 
is far better than any of those previously described. For a 
telescope of any size, an equatorial mounting is highly desir- 
able, because the Earth is in rotation. 

The spinning of the Earth from west to east means that 
all the celestial bodies appear to move from east to west. This 
movement is slow, judged by everyday standards, but when we 
use a telescope to magnify the size of an object in the sky we 
also magnify the apparent 
motion. If the telescope re- 
mains stationary, a star or 
planet will seem to shift steadily 
across the field until it dis- 
appears from view. The tele- 
scope has then to be moved 
until the object is found again. 
Moreover, there are two mo- 
tions to be made : up or down 
("declination"), and east to 
west ("right ascension"). Slow 
motions of the type shown in 
Fig. ri provide one answer, 
and are helpful, but it is irri- 
tating to have to fiddle con- 
tinuously with both wheel and 
handle. To work in comfort 
under such conditions, one 
would need four or five hands. 

In the equatorial stand, the 
"polar axis" is pointed to- 
wards the celestial pole, so that 
only the east-to-west pushing 

is necessary — the telescope will take care of the up-or-down 
motion of its own accord. If possible, a driving motor should be 
attached, regulated so that the telescope moves slowly round at 

Fig. 12. Simple tripod mount 
for a small refractor. 


a speed which compensates for the apparent shift of the celestial 
bodies across the sky. 

All these stands can be made. Even the driving clock presents 
no insuperable difficulties, and in the case of a small telescope 
a drive can be adapted from an old gramophone motor. The 
books listed in Appendix XXXII will be found to give all the 
instructions needed. 

However, there are some people who are hopelessly clumsy 
with their hands, or who have no wish to spend hours in the 
messy, delicate process of mirror-grinding or building a stand. 
There is no disgrace in this (at least, I hope not!) ; one cannot 
do everything, and the solution is to buy a telescope ready 
made, so that it can be put to use at once. 

What often happens is that 
the would-be buyer visits a 
dealer and examines an array 
of sleek, impressive-looking 
refractors. He learns that a 
3-inch costs over £Bo, while 
a 5-inch runs into at least 
£600. He is discouraged, and 
unless he has the sense to ask 
for advice his astronomical 
career may end there and 

Of course, the casual star- 
gazer who is prepared to 
spend a substantial sum will 
gain much pleasure from a 
3-inch, even if it is mounted 
upon a pillar and claw. The 
instrument will look impos- 
ing if it is stood In one corner 
of the library, and it will 
serve to give adequate small-scale pictures of the Moon, the 
satellite system of Jupiter and the rings of Saturn, as well as 
rich star-fields in the Milky Way. However, few people want to 
spend £Bo or more for the sake of occasional amusement, and a 
smaller instrument, such as a 2-inch retractor, is of little use 
astronomically. Moreover, even a 2-inch costs upwards of £20 


Fig. 13. Pillar and Claw mount 
for a small refractor. I have nick- 
named it the "Blancmange" 
mount, for reasons which should 
be obvious to anyone who has 
used it. 


if bought new, plus extra sums for essentials such as stands, 
focusing arrangements and eyepieces. A word of warning is 
necessary here. It is of no use whatsoever trying to use any 
telescope for astronomical purposes unless it is fitted with a 
stand of some kind. Any sort of stand is better than nothing.* 

Though new refractors are expensive, it is sometimes possible 
to pick up a cheap second-hand 3-inch. Anyone who is prepared 
to make regular visits to junk shops stands a fair chance of 
finding such an instrument eventually, and it is also worth while 
to keep a close watch upon the advertisement columns of 
newspapers and periodi- 
cals. There is no guaran- 
tee of rapid success, but 
a 3 -inch refractor is an 
excellent instrument for 
the beginner, provided 
that it is firmly mounted. 
Once the user has gained 
experience, he will be 
ready to change to some- 
thing larger. 

Refractors are easy to 
handle, but they are not 
light, and a 4-inch is the 
limiting size for porta- 
bility. A larger instru- 
ment needs a permanent 
home, preferably some 
kind of run-off shed or 
observatory. Few 4-inch 

AB- declination axis. 
Fig. 14. Equatorial mount. 

refractors are to be found second-hand, and in the ordinary 
way the cost of a new instrument is prohibitive. 

Reflectors are cheaper, and are much more portable, 
particularly when fitted with skeleton tubes. Here again the 
cost of a complete new instrument is rather high, but second- 
hand reflectors of from 6- to 8-inch aperture can be found 
quite frequently. The beginner with £50 to spend may indeed 

* Some time ago, I had a letter from a beginner who had a 2-inch refractor and 
was disappointed with its performance. As soon as he mounted it upon an im- 
provised stand, he found that it worked very well, 



have the choice between a new 2-inch refractor, or a second- 
hand 6-inch reflector; obviously, he will do far better to buy 
the reflector, even if it needs repairing. In my view there is 
no point in spending much money on a small refractor of 
aperture 2 inches or less, unless it is to be used only for occasional 

It is wise to be careful when buying a second-hand telescope, 
particularly a reflector. It may look perfectly sound, with 
polished fittings and a beautifully-painted tube; but if the 
mirror is poor, the performance also will be poor, and defects 
in a mirror do not always show themselves at first sight. Of 
course, one way of deciding is to make a practical test upon a 
star image ; but if the telescope lacks a usable stand, or needs 
adjusting, this may not be possible, in which case the only 
safeguard is to seek advice from somebody who has a sound 
knowledge of optics. The beginner who spends pounds upon 
a second-hand reflector only to find that the mirror is of 
no use is unlikely to receive much sympathy — nor will he 
deserve it. 

Let us assume, then, that we have managed to acquire a 
telescope. What care must be taken of it, and what extra 

equipment shall we need ? 
One addition is simpli- 
city itself. A small sight- 
ing telescope or "finder" 
can be fitted, and will be 
found most useful (Fig. 
15). Even a toy telescope 
will do, and can be at- 
tached by Meccano. The 
advantage of a finder is 
that it has a large field 
of view, and will save 
much time when a faint 
object is being searched 
for. The object is simply 
brought to the centre of 
the finder field; if the 
adjustments are correct, 
the object will then be visible in the field of the main telescope. 


Fig. 15. Fitting a finder to 
a reflector. 


A finder is not strictly necessary; but it is so cheap, and so easy 
to fit, that it seems a pity not to have one. 

More important is the dew-cap, which is simply a short 
tube which fits over the object-glass end of the refractor in 
order to prevent dust, dirt and dew from settling on the lens. 
It can be made from a cocoa-tin lined with blotting paper, or 
something of the kind, and a cap should always be kept over 
the object-glass when the telescope is not actually in use 
(Fig. 16). 


Object Glon 

Dew Cap 


Fig. 16. Dew-cap for a refractor. 

If the object-glass needs cleaning, it should be brushed very 
gently with a camel's-hair brush and then wiped even more 
gently with a piece of very fine, clean silk or wash-leather. To 
take the various components of an object-glass apart is most 
unwise unless the owner has a really good idea of what he is 
about. All things considered, a small refractor should need little 
or no attention for years on end, provided that it is not roughly 
handled. When some major adjustment does become necessary, 
it will be worth while to take the whole instrument to an expert. 
It is better to spend a little money on maintenance than a great 
deal of money on buying a new telescope. 

Reflectors need more attention. The main mirror and the 
flat need periodical re-silvering, and although this can be 
done at home it does need a good deal of care. It is probably 
better to have the mirror aluminized, which will give a much 
longer period before anything further need be done; rhodium 
coating can also be used. Both mirror and flat should be kept 
covered with a protecting cap except when actually in use, 
and yet another word of warning may be timely here. Before 
using the telescope, uncap the flat before you expose the main 
mirror. I know of one luckless observer who uncovered the 
main mirror first — and then dropped the flat cover on to it. He 
spent the next few months grinding himself a new mirror. 



Eyepieces are vitally important, since using a good telescope 
with a bad eyepiece is like using a good record-player with a 
bad needle, Theoretically (though not always in practice) 
eyepieces arc made to a standard thread, so that any eye- 
piece should fit any telescope; but the magnification obtained 
depends upon the focal length of the mirror or object-glass, 
so that an eyepiece which yields X 50 on a 3-inch refractor will 
not yield X 50 on a 6-inch. Moreover, eyepieces are of various 
types, adapted for different types of telescopes. 

It is advisable to have at least three eyepieces. One should 
give low magnification, for star-sweeping and general views; 
the second, moderate magnification for more detailed views of 
planets and some stellar objects; the third, high magnification 
for use on really good nights. For my 3-inch, f/12 refractor I 
have found that suitable magnifications are 36, 72 and 144, 
while for a 6-inch reflector the corresponding powers might 
be 50, 120 to 180, and 300 to 360. Individual observers 
are bound to have their own ideas on the subject. 

One thing is however important: Do not try to use too 
high a power. If the image becomes even slightly blurred, 
change at once to a lower magnification. It may be impressive 
to say that an observation was made " X400" or " X500", but 
it will often be found that a smaller, sharper picture will yield 
far more detail. 

Let us sum up what has been said. If a telescope is to be 
bought, it will be far better to search for a moderate reflector 
than to spend a large sum of money on a portable refractor. 
Never buy a telescope until you have had an expert opinion on 
it, since although it may look sound it is quite likely to be 
useless. Most important of all, do not trust your own judgement 
unless you are sure that you are really competent. Search in 
second-hand shops and advertisement columns until you find 
something that you think will suit you; see it; have it checked; 
and if you are satisfied, buy it. 

A favourite mistake is to poke a telescope through the 
bedroom window in the expectation of seeing fine detail on the 
Moon or a planet. Actually, good results can seldom or never 
be obtained in any such way. The temperature of the room is 
almost certain to be higher than that outside, and the resultant 
air-currents will destroy the sharpness of the image. Moreover, 



there arc other hazards. In my very early days I tried to 
observe from the warmth of my bedroom, and dropped an eye- 
piece fifteen feet on to a gravel path. 

A portable telescope on a tripod is easy to carry about, but a 
reflector larger than 8-inch aperture or a refractor larger than 
4 inches is generally too heavy to be moved far. This means 
that it must be set up in one permanent position, and should be 
protected against the weather. 

If the telescope is carefully painted it may not come to 
much harm, and one easy solution is to provide it with a water- 
proof cover. A run-off "observatory" is simple to build; it can 
be run on rails, so that when the telescope is to be used the 
whole shed can be rolled back out of the way. It may be either 
centrally divided or else made in one section. 

A proper observatory is built in the form of a dome, one 
section of which can be removed, either by taking it out or by 
swinging it back on hinges. The dome can be revolved, gen- 
erally by being pulled round with ropes. Here again the prob- 
lems are purely practical, but a dome is by far the best form of 
observatory, partly because it protects the telescope completely 
and partly because the observer is shielded from the chill 
breeze of a winter night. 

The great observatories of the world are among mankind's 
finest creations. Pride of place must go to that on Falomar 
Mountain, in California, where the main instrument is the 
200-inch Hale reflector, named in honour of Professor George 
Ellery Hale, who was the moving spirit behind its construction. 
Since its completion, a quarter of a century ago now, the Hale 
reflector has caused a real revolution in astronomical thought. 

A vast reflector costs a fabulous sum, not only because of the 
optical parts but also because of the extra equipment needed. 
An observatory such as Palomar is almost a city in itself. 
There are instruments of all types, each in its own dome; 
laboratories; dark rooms; living quarters and lecture theatres. 
At Palomar, the 200-inch may be the main instrument, but 
there are many others as well. 

Most great telescopes are set up in observatories high above 
sea-level. This is because the atmosphere, so necessary to fife, 
is a positive handicap from the astronomer's point of view. Not 
only is it dirty, but it is also turbulent, so that using a high 



magnification will result in violent unsteadiness of the image. 
The densest part of the air-mantle is concentrated near the 
Earth's surface, and by climbing as high as possible we can 
reduce the disturbance, though we can never really cure it. 

Greenwich Observatory, so familiar a name to all of us, 
has had to contend with extra problems. When Sir Christopher 
Wren designed the original structure, in the reign of Charles 
II, Greenwich was a village well outside London; there were 
few artificial lights, and the air was clear and smoke-free. 
Nowadays the situation is very different. London's tentacles 
have stretched out, and Greenwich has become a suburb. 
Electric lamps cause a glare across the sky, while the smoke 
from a thousand factory chimneys causes an everlasting pall. 

Modern Greenwich is, in fact, no place for a large telescope. 
When it was proposed to build a 98-inch reflector, only slightly 
smaller than the Mount Wilson colossus, a decision had to be 
made. To set up a vast instrument in a smoky atmosphere 
would be pure folly, and so it was agreed to move the whole 
observatory to Herstmonceux, near the little Sussex town of 
Hailsham, where seeing conditions were still relatively good. 
The war held matters up, and the move took a very long 
time, but by the beginning of 1957 there was little left at 
Old Greenwich apart from historical relics. Perhaps the most 
interesting of these relics is the Octagon Room, where John 
Flanisteed worked away at his famous star catalogue. Still to be 
seen there is the "transit telescope" built by Edmond Halley, 
who succeeded Flamsteed and became the second Astronomer 
Royal. There is also an interesting "Herschel Room". Mean- 
while, the 98-inch reflector is being shifted to a better observing 
site in the Canary Islands. 

Making a 200-inch mirror is difficult enough, but making 
a 200-inch object-glass would be quite out of the question, even 
if it could be mounted satisiactorily. The largest refractor in 
the world is the 40-inch at Yerkes, in the United States, while 
the largest in Europe is the 33-inch at Meudon, between Paris 
and Versailles. The Meudon instrument itself is over 70 feet 
long; I have had the privilege of making extensive lunar 
observations with it, and so have personal experience of its 
high quality. The 22-inch refractor at the Pic du Midi, in the 
French Pyrenees, is another great telescope, and since it lies 



at a height of 10,000 feet it can be used under conditions of 
great clarity. It is true to say that the lunar and planetary 
photographs taken there are among the best that have ever 
been produced by an observatory on the surface of the Earth. 

Of course, the coming of the Space Age has caused a change 
of outlook. No Earth-based photograph of the Moon or Mars 
can compare with a picture sent back from a space-probe, and 
there are many investigations which cannot be carried out from 
ground level simply because the atmosphere acts as a screen; 
for instance, we cannot study the short-wave radiations from the 
sky which we call X-rays, because they are blocked out. For 
X-ray astronomy, it is necessary to send equipment above the 
obscuring layers of atmosphere. 

Telescopes have already been sent up in rockets, and, of 
course, in the first true space-station : America's Skylab of 1 973. 
If all goes well, we may hope that before the end of the century 
there will be observatories on the surface of the Moon. Such 
an idea would have seemed "science fiction" only a few decades 
ago, but there is nothing far-fetched about it today. 

Where, then, does this leave the amateur observer? In my 
view, it leaves him exactly where he has always been. He (or 
she) can still enjoy the night sky, and can still make contribu- 
tions which are really useful. Let me again stress that although 
a major telescope is highly desirable, it is not essential, at least 
for some branches of research. And if you have a limited 
amount of money to spend (less than £30, say}, I would 
recommend buying a pah* of good binoculars rather than a 
telescope. If you spend between £10 and £15 on binoculars — 
for instance, of the 7 x 50 type (magnifictaion 7, aperture of 
each object-glass 50 millimetres) you will be able to have mag- 
nificent views of objects such as star-clusters. I have always 
maintained that binoculars are more valuable than a very 
small telescope, though not everybody will agree. In any case, 
there is plenty of choice; and astronomy is open to all. 


Chapter Four 


Some people refuse to take an interest in astronomy 
simply because they arc frightened of it. They cannot appre- 
ciate distances of millions of miles; they cannot believe that 
each star is a sun, and their minds remain firmly anchored to 
the Earth. 

This point of view is commoner than might be imagined, 
and part of the difficulty originates from the vast scale of the 
universe. Nobody can really picture "a million miles", and the 
tremendous heat of the Sun's interior is equally beyond the 
human brain. The best way to give some account of scale is to 
visualize a model, which will at least put our ideas in some sort 
of order. 

The Solar System in which we live is made up of one star 
(the Sun) j nine major planets, and numerous bodies of lesser 
importance, such as the moons or "satellites", the minor 
planets, the meteors and the comets. Returning to the model 
discussed on page 30, we imagine that the Sun has become a 
globe only 2 feet in diameter, so that we can put in the rest of 
the planets on the correct scale. Mercury will become a grain 
of mustard seed 83 feet from the 2-foot Sun; Venus, a pea at 
156 feet; the Earth, another pea at 215 feet; Mars, a pin's 
head at 328 feet; Jupiter, an orange at \ of a mile; Saturn, 
a tangerine at | of a mile; Uranus, a plum at \ of a mile; 
Neptune, another plum at i\ miles; and Pluto another pin's 
head, with a maximum distance of 2 miles. The nearest of 
the ordinary stars will then lie 10,000 miles off, which gives us 
a good idea of how isolated the Solar System really is. 

There is a great deal of difference between a 2-foot globe 
and an orange, and so even Jupiter, largest and most massive 
of the nine planets, is by far inferior to the Sun, The Sun is in 
fact the absolute ruler of our system ; it controls the movements 
of the planets, and the planets depend entirely upon solar heat 
and warmth. No planet has any light of its own. Even Venus, 



the glorious "evening star" which can shine down like a small 
lamp and can even cast a shadow at times, is in itself a 
non-luminous body. 

One thing is evident from our scale model: the planets 
can be divided into two well-marked groups. The inner group 
is made up of four small and comparatively close-in worlds, 
Mercury, Venus, the Earth and Mars. Then comes a wide gap, 
followed by the four giants, with that curious little world 
Pluto on the very fringe of the Sun's kingdom. Actually, the 
gulf between Mars and Jupiter is not empty. It is occupied 
by many thousands of tiny bodies, the Minor Planets or aster- 
oids, which would be mere grains of dust on the scale which we 
have chosen. 

The individual motions of the bright planets have been 
known since very early times, and the very word "planet" 
means "wandering star". The ancients also noticed that the 
planets keep strictly to a certain region of the sky, which they 
named the Zodiac. The reason for this is that the paths or 
"orbits" of the planets He almost in the same plane, so that when 
we draw a plan of the Solar System upon a piece of flat paper, 
as in Fig. 17, we are not very far wrong. Consequently, the 
planets can be seen only in certain directions, and this limita- 
tion applies also to the Sun and the Moon. The Sun's apparent 
yearly path among the stars indicates the "ecliptic". 

A good way to make this clear is to imagine that we are 
standing in a wood, looking at low trees around us. There may 
be trees to all sides, but no trees will appear in the sky or 
beneath our feet — because the trees lie in roughly one plane, 
the plane of the Earth's surface. 

As we know, the stars were originally looked upon as 
mere points of reference. The early astronomers grouped them 
into constellations, and there are twelve constellations in the 
the Zodiacal band, which stretches right round the heavens. 
The most famous of these groups is probably Aries, the Ram. 
It contains no very bright stars, and is not particularly easy to 
identify, but in the far-off times when the Ghaldasan shepherd- 
astronomers gazed at the skies during their night watches 
Anes was the constellation in which the ecliptic cut the 
celestial equator", the projection of the Earth's equator upon 
the celestial sphere. Actually, the point of intersection, or 



"First Point of Aries", has moved since then, because of the 
wandering of the polar point, and has now passed into the 
neighbouring constellation of the Fishes; but we still keep to 
the old term. 

Since the planets are 
never far from the ecliptic, 
they are easy to recognize. 
In any case, Mars (when 
at its brightest) and Jupiter 
are so distinctive that they 
cannot possibly be confused 
with stars, while Mercury 
and Venus, which are closer 
to the Sun than we are, 
have their own way of be- 
having. Only Saturn, and 
Mars when at its faintest, 
cannot be identified at the 
most casual glance. 

The first astronomer to 
give a proper description of 
the way in which the planets 
move was Johann Kepler. 
Between 1609 and 1619 he 
published his three famous 
Laws of Motion, which are 
interesting enough to des- 
cribe in slightly more detail. 
They are as follows: 

Law 1 . The planets move in 
ellipses, with the Sun at 
one focus. 


Fig, 17. A: Orbits of the 

Inner Planets. 
B: Orbits of Mars and the five 

Outer Planets. 

Law 2. The radius vector 
(the line joining the centre 
of the planet to the centre 
of the Sun) sweeps out equal areas of space in equal times. 

Law 3, The square of the sidereal period is proportional to 
the cube of the planet's mean distance from the Sun. 

5 2 


These may seem rather complex, but really they are quite 
simple. Law 1 requires no explaining; the only point to bear 
in mind is that although the orbits of the planets are ellipses, 
they are of slight eccentricity, and do not depart much from 
the circular form. It is the other two Laws which sometimes 
cause beginners to wrinkle their brows. 

Law No. 2 is explained by the diagram in Fig. 18. The 
figure is not to scale, and the orbit of our supposed planet P 
is much more eccentric than is actually the case with any major 
planet in the Solar System, but one has to make the diagram 

Fig. 18. Kepler's Second Law. 

inaccurate in order to make it clear! S is the Sun; P, Pi, P2 
and P3 stand for the planet in various positions in its orbit 
round the sun. 

Assume that the planet moves from P to Pi in the same 
time that it takes to go from P2 to P3. Then the shaded 
area of PSPi must be equal in area to the dotted area of 
P 2 SP 3 . Since the dotted area is "longer and thinner", it is 
clear that the planet is moving at its quickest when closest to 
the Sun, 

This fact is vitally important. It can be summed up by the 
simple rule "The nearer, the faster". The Law does not mean 
only that a planet moving in an elliptical orbit must travel at a 
varying speed; it means also that a planet when close to the 
Sun must move faster than when it is more distant. This is 
->ome out by direct measurement. Mercury, for instance, 
has an orbit which is definitely eccentric, so that at its closest 
to the Sun ("perihelion") it is only 28^ million miles away, 



as compared with 43^ million miles at its farthest point 
("aphelion"). The orbital speed varies from 36^ miles per 
second at perihelion to only 24 at aphelion. The Earth, at the 
greater distance of 93 million miles, is a comparative sluggard, 
and has an average rate of a mere 184 miles per second. 

The Third Law leads to some equally important conclusions. 
The "sidereal period" of a planet, the period taken to complete 
one revolution round the Sun — the planet's "year" — is linked 
with the actual distance from the Sun, and if we know the one 
we can find the other. 

The Earth's sidereal period is 365J days. By studying the 
way in which the other planets seem to move, we cam find out 
their respective periods, which range from 88 days for Mercury 
to slightly less than 248 terrestrial years in the case of Pluto. 
Once this has been done, we can draw up a complete model of 
the Solar System in terms of the "astronomical unit", the dist- 
ance between the Earth and the Sun. 

To turn these relative distances into actual miles, all that is 
needed is any one precise measurement. If, for instance, we 
could obtain an accurate figure for the distance of Venus, the 
length of the astronomical unit could be calculated. Since 
1 96 1 radar methods have been used by both the Americans 
and the Russians, the general principle being to "bounce" an 
energy pulse off Venus, time the delay before the "echo" 
returns, and then calculate the distance travelled — remember- 
ing that a radar pulse, like visible light, moves at 186,000 miles 
per second. It is now thought that the mean Earth-Sun distance 
amounts to approximately 92,957,000 miles. 

The Moon, which revolves round the Earth,* is of special 
interest to us. Everyone is familiar with its monthly phases, 
from new to full and back again to new, but not everyone is 
sure how they are caused. Some people still believe that they 
are due to the shadow of the Earth, but the true explanation 
is far simpler. 

The Moon is a dark body, shining only by reflected sunlight. 
As the Sun can light up only one half of the lunar globe at a 
time, the other half must be non-luminous, and therefore 

• Actually, the Earth and Moon revolve round their common centre of gravity; 
but as this point lies within the terrestrial globe, the plain statement that "the 
Moon revolves round the Earth" is good enough for most purposes. 



invisible. In Fig, 19, the Moon is shown in four positions in its 
monthly journey — Mi to M4, At Mi, the dark side is turned 
towards us; since this does not shine, the Moon is invisible, or 
new. As the Moon moves on towards M2, a little of the day 
hemisphere starts to turn in our direction, and we see the 
familiar crescent shape ; by the time M2 is reached, half the 
sunlit side is presented, and the Moon is at half phase. (Rather 



Fig. 19. Phases of the Moon. S — Sun; E — Earth; Mi to 
M4 — the Moon in four different positions in its orbit. Not 

to scale. 

confusingly, this is termed First Quarter — because the Moon 
has completed roughly one quarter of its orbit from new to 
new.) Between M2 and M3 the appearance is "gibbous", 
between half and full, and by the time M3 is reached the Moon 
shows us the whole of its day hemisphere. After Full, the phase 
wanes once more, to half-moon at M4 {Last Quarter) and then 
crescent, until Mi is reached at the next new moon. 

Clearly, the Earth's shadow has nothing to do with these 
phases. It is true that when the Moon is full (M3) and the 
three bodies are perfectly lined up, the shadow of our globe 
does fall across the Moon, causing a lunar eclipse ; but eclipses 
do not occur every month, because the Moon's orbit is some- 
what tilted with respect to ours. 

The lunar phases must have been known since the dawn of 
history, but it was not until the invention of the telescope that 
Venus and Mercury were found to behave in a similar way. 



The phases of Venus, first detected by Galileo, are explained 
by Fig. 20. E represents the Earth, which is assumed to be 
stationary (really, of course, it is moving round the Sun all 
the time, but this makes no difference to the illustration); 
S the Sun, and Vi to V4 Venus in four different positions. 
Since Venus is closer to the Sun than we are, and moves more 
quickly, it completes one circuit in only 224*7 terrestrial days. 




Fig. 20. Phases of Venus. S— Sun; E— Earth; Vi to V4— 
Venus in four different positions in its orbit. Not to scale. 

At Vi the Earth, Venus and the Sun are in a straight 
line, with Venus in the middle. The night side is then turned 
towards us, and Venus is new, so that it cannot be seen at all. 
This position is known as "inferior conjunction". Occasionally 
the alignment is perfect, and Venus can be seen as a black spot 
against the solar disk; but since Venus too has a tilted orbit, 
these "transits" are rare. The next wOl not occur until the 
year 2004. 

As Venus moves on towards V2, we start to see the sunlit 
side. The planet appears in the morning sky as a slender 
crescent, becoming brighter and brighter as it draws away from 
the line of sight with the Sun. At V2 the three bodies form a 
right-angled triangle, so that Venus appears as a half disk. 
It then rises some hours before the Sun, and is a splendid 
object in the east before dawn. The technical term for this is 
"Western" or Morning Elongation. 

As it travels towards V3, Venus changes from a half into a 



gibbous disk, and draws back towards the direction of the 
Sun so that it grows steadily less conspicuous. By the time 
it has reached V3, it has ceased to be visible except during the 
hours of daylight. It is then at "superior conjunction", and 
since it lies almost behind the Sun it is not easy to find even 
with a telescope. 

After passing superior conjunction, Venus makes its appear- 
ance low down in the evening sky, shrinking gradually to a half 
as its angular distance from the Sun grows. It reaches eastern 
elongation at V4, and is then at half-phase once more, after 
which it narrows to a crescent as it returns to inferior con- 
junction at Vi. 

The "synodic period" of Venus, the interval between one 
inferior conjunction and the next, is 584 days, though this may 
vary by as much as four days either way. The interval between 
its appearance at V4 and that at V2 is about 144 days, while 
440 days are needed for the much longer interval between the 
appearance at V2 and that at V4, 

Venus is of course at its closest to the Earth at inferior 
conjunction. The distance is then reduced to about 24 million 
miles, about a hundred times as great as that of the Moon; 
but as the dark side is then almost wholly presented, we cannot 
see the planet at all. When the disk is almost fully illuminated, 
Venus is a long way away. It is in fact a most infuriating object 
to observe. 

Mercury behaves in the same manner as Venus; but since 
it is smaller, as well as being closer to the Sun, it is much less 
easy to study. It is never conspicuous to the naked eye, and only 
at favourable elongations can it be seen glittering near the 
horizon like a star. This is interesting, in view of the fact that 
many people believe that planets cannot twinkle. It is true that 
a planet, which shows a definite disk, twinkles much less than a 
star, which appears only as a minute point of light ; but when 
a planet is low down, and thus shining through a dense layer of 
atmosphere, it may twinkle violently. This is particularly so in 
the case of Mercury. 

The remaining planets lie beyond the Earth in the Solar 
System, and cannot appear as halves or crescents. Mars is shown 
in the diagram (Fig. 21}, and is typical of all the rest. 

Let us start with the Earth at Ei and Mars at Mi. The 



Sun, the Earth and Mars are lined up, with the Earth in the 
middle; Mars is therefore directly opposite the Sun, and is 
at "opposition". One year later, the Earth will have completed 
one revolution, and will have arrived back at Ei; but Mars, 
moving more slowly in a larger orbit, will not have had time to 
get back to Mi, It will have travelled only as far as M2, 

and will lie on the far side 
of the Sun, badly placed for 
observation. The Earth has 
to catch it up, with Mars 

all the 

Fig. ai. Oppositions of Mars. Ei 
and Mi — positions of Earth and 
Mars at the oppositions of Septem- 
ber 1956; E2 and M3 — positions 
at the opposition of November 
1958. There was no opposition of 
Mars in 1957. 

moving onwards 
time, and on an 
780 days elapse before the 
three bodies are lined up 
again. The 780-day interval 
between successive opposi- 
tions is therefore the synodic 
period of Mars. 

The giant planets are 
much more remote, and 
move so much more slowly 
that the Earth takes less 

time to catch them up. 
Jupiter's synodic period is 
399 days, while in the case of far-off, sluggish Pluto the period 
is 366I days. After having completed one circuit of the Sun, the 
Earth has to travel on for only an extra day and a half before 
it catches up with Pluto. 

Each of the nine major planets has its own characteristics. 
The members of the inner group are small, solid bodies; all 
have appreciable atmospheres, with the exception of Mercury; 
and there is still a faint probability that low forms of life 
flourish on Mars. The giants, however, are built up on a very 
different pattern. When we look at Jupiter or Saturn, what we 
see is not a solid, rocky globe, but the outer layer of a deep 
"atmosphere" made up of poisonous gases. Pluto presents 
problems of its own, but since it is so faint and so far away it is 
not of much interest to the amateur. 

Most of the planets have moons, or satellites. The Earth, of 
course, has one; Jupiter boasts of fourteen, Saturn ten, Uranus 



five and Neptune and Mars two each, while Mercury, Venus 
and Pluto do not seem to possess any. A small telescope will 
show the brightest of these satellites, and a few exceptionally 
keen-sighted persons are said to have seen one or two of the 
chief satellites of Jupiter without a telescope at all. 

The minor planets, or asteroids, swarm in the wide gap 
between the orbits of Mars and Jupiter. All are dwarf worldlets, 
less than 800 miles in diameter, and only one (Vesta) is ever 
visible without optical aid. Even with a telescope, they look 
remarkably like small stars, and the only way to identify them 
is to watch them from night to night, until their slow movement 
across the starry background betrays their true nature. 

Halley's Comet 



Fig. 2a. Orbits of Saturn and Halley's Comet. 

The remaining members of the Sun's family are much less 
substantial. Particularly interesting are the comets, which have 
been termed the stray members of the Solar System. Most of 
them move in elliptical orbits, but their orbits are much more 
eccentric than those of the planets. Fig. 22 shows the path of a 
periodical comet (Halley's) as compared with the orbit o 
Saturn. Nor is a comet a solid body; it is made up of a swarm 
of particles contained in an envelope of very thin gas. A 
famous astronomer once called comets "airy nothings", and 
though they are not "airy" in the usual sense of the word they 
arc certainly flimsy. Comets may be of immense size, but they 
are of negligible mass, and they are of course completely 
harmless, even though they still strike terror into the hearts of 
some of the Earth's backward races. 

The ghostlike nature of a comet means that it can be seen 
only when it is fairly close to the Earth and to the Sun. Halley's 
Comet— named after Edmond Halley, Flamsteed's successor 



at Greenwich, who was the first to discover that it revolves 
round the Sun — has a period of 76 years, but for most of that 
time it is too faint to be seen. It last came to perihelion in 
19 10, in the reign of Edward VII, and will not reappear until 
1986. We know where it is, but at present we cannot observe it. 

Other comets have shorter periods, and can thus be seen every 
four or five years. Others, however, have periods of many 
centuries. Each year brings forth its quota of new faint comets, 
though not many of them become bright enough to be seen 
without the aid of a telescope. 

^ Meteors, or shooting-stars, are also members of the Solar 
System. The name is misleading, since they are not stars at all. 
They are small pieces of matter travelling round the Sun in 
elliptical orbits, and in the ordinary way they are too faint to be 
seen. Sometimes, however, a meteor may come close to the 
Earth, and if it is moving at the right speed in the right 
direction it will naturally encounter the Earth's mantle of air. 
It will then plunge into the upper atmosphere, and will rub 
against the air-particles, setting up friction; first it will become 
warm, then hot, and then it will burst into flame, usually 
burning itself completely away in a matter of seconds and 
finishing its earthward journey in the form of fine dust. 

It is easy to prove that air sets up resistance. If you cup your 
hand and swing it abrupdy, you can feel the pressure; a stick 
hisses through the air if swished, and the friction against the air 
causes a certain amount of warmth. Small wonder that a 
meteor, travelling at a tremendous speed, will become violently 
heated. Above a height of 120 miles or so, the air is of course 
too thin to cause appreciable resistance. 

Such is the Solar System. It contains bodies of all kinds, from 
the vast, intensely luminous Sun down to tiny particles of 
interplanetary dust, and even though it may be unimportant 
in the universe as a whole it is of supreme importance to 

Yet there has been a decided change of attitude during the 
past few years. Previously, professional astronomers were busy 
with their studies of the greater universe, and paid scant 
attention to the surfaces of the Moon and planets; so far as 
the lunar craters or the Martian deserts were concerned, the 
amateur was left a clear field, which is why so much of our 



present-day knowledge is based upon amateur work. Then, in 
1957) the first earth satemte was launched, and the Space Age 
began. From being a remote body of interest only to a few 
enthusiasts, the Moon became officially accessible, with Mars 
and Venus next on the astronautical list. One must admit, 
with regret, that military planning had something to do with 
the change of view. A rocket that can launch a lunar probe 
can also launch a nuclear bomb. 

The first successful Moon-rockets were launched by the 
Russians in 1959, but it was not for some years afterwards that 
lunar mapping from space-probes was really under way. By the 
mid-1960s detailed charts had been compiled— without which, 
of course, the Apollo landings of 1969 could never have been 
attempted. Meanwhile, Mars had also been by-passed, and 
pictures sent back from the Mariner vehicles showed that the 
Martian surface, like that of the Moon, is cratered. 

During the 1970s rapid progress was made; Mars was studied 
in detail, and two Viking probes came down on to the surface 
of the planet so that they could transmit data, while the 
Russians even managed to obtain two pictures direct from the 
hostile surface of Venus. Mercury was surveyed by a Mariner 
probe, and was found to be cratered. Two Pioneers by-passed 
the giant world of Jupiter, and as I write these words (February 
1978) Pioneer 11 is en route for Saturn, while two Voyager 
vehicles have begun a journey which should take them past 
both Jupiter and Saturn. 

All this is scientifically excellent, because it has led us on to a 
much better understanding of our neighbour worlds. It means, 
of course, that amateur work so far as these bodies are con- 
cerned has lost much of its value; but nobody need be despon- 
dent. It may be centuries before space-travellers are able to 
enjoy close-up views of the belts and moons of Jupiter or the 
superb ring-system of Saturn, and in any case die surfaces of 
these giant worlds are always changing, so that continuous 
observation of them is of the utmost value. The overall situation 
was aptly summed up recently by a friend of mine to whom I 
was talking at an astronomical meeting. "Yes," he said 
thoughtfully. "The scope is more limited now, but this makes 
no difference to the enthusiastic amateur. We may have lost 
Mars and the Moon, but there's plenty left!" 


Chapter Five 


Studying the sun calls for methods different from those 
used in any other branch of astronomy. In other cases, the main 
problem is to collect as much light as possible; with solar 
observation there is plenty of light available, but it is highly 
dangerous to look directly at the Sun's disk using a telescope, 
as the eye of the observer is certain to be damaged. 

The Sun's diameter is 865,000 miles, 109 times that of 
the Earth. But though the solar globe could contain over a 
million bodies the size of our own world, it does not contain 
the mass of a million Earths. Only 332,000 Earths would be 
required to make one body with the mass of the Sun. This means 
that the Sun is less massive than one might expect from its 
size, and that the mean density is less than that of the Earth 
— in fact, only 1 -4 times as great as that of water. 

Of course, this is not the uniform density throughout the 
solar globe. Density increases with depth. Near the centre of 
the Sun, the material is denser than steel, even though it is still 
technically a gas, whereas the outermost parts of the Sun are 
more rarefied than the best vacuum we can produce in terres- 
trial laboratories. 

The gravitational force that would be felt by a man standing 
on the surface of a globe depends upon two factors, the mass 
and the size. Taking the Earth's surface gravity as unity, the 
surface gravity of another body can be found by dividing the 
mass by the square of the radius. For the Sun, these figures are 
respectively 332,000 and 109, so that the surface gravity is 
332,000 divided by 109 squared, or 28. A man who weighs 
14 stone on Earth would weigh 2 \ tons if he could be taken to 
the surface of the Sun, so that he would not even be able to 
stand upright; he would be crushed by his own weight. How- 
ever, there is no prospect of life, human or otherwise, surviving 
on the solar surface. Even one of the tough, grizzled space- 
captains of science fiction would feel uncomfortably warm 
there, since the temperature amounts to 6,000 degrees. 



The great size and the low density mean that the Sun 
cannot be a solid body like the Earth. It is in fact made up 
entirely of gas, though deep down inside the globe this gas is 
under tremendous pressure — at least a thousand uillion 
atmospheres — and behaves therefore in a decidedly un-gaslike 
manner judged by our normal standards. 

Telescopic views of the Sun do not tell us much more. 
Interesting features can be seen, such as the dark spots and the 
brighter patches or faculae, but for more serious studies it is 
necessary to use special instruments. Some of these can be 
made by the skilled amateur, but to describe them would be 
beyond the scope of the present chapter, and all that can 
be done here is to summarize the results obtained by them. 

Newton was the first to explain the breaking-down of 
white light into its constituent colours. What he did was to cut 
a small hole in the shutter of his window, so that only a narrow 
beam of sunlight could pass through. This beam entered a glass 
prism, and the resulting rainbow or spectrum was spread out on 
the far wail. Later, Newton improved the experiment by using 
a slit instead of a hole, and by putting a lens between the prism 
and the wall so that he could bring the colours to a sharp focus. 

Newton never took his investigations much further, probably 
because his prisms were of poor quality glass. The next develop- 
ment was due to Fraunhofer, who returned to the problem in 
1 8 14, and who found that the spectrum of the Sun is crossed by 
numbers of dark lines of different degrees of intensity. It is 
now known that each of the Fraunhofer Lines is due to the 
effect of one definite substance, and this is the basis of all solar 
and stellar spectroscopic work. One substance (such as iron) 
may produce many characteristic fines. 

It may be added that dark fines had been seen in 1802 by a 
British scientist, Wollaston. Wollaston did not however 
realize their importance, and thought that they merely marked 
the boundaries of the different spectrum colours, so that the 
main credit must go to Fraunhofer. 

All matter in the universe, whether in the Earth, the Sun 
or the remotest star, is made up of different combinations of a 
small number of fundamental "elements". There are 92 
familiar elements, hydrogen being the lightest and uranium 
the heaviest; since they form a complete series there is no 



chance of our having missed one. No new elements can exist, 
because there is no room for them in the sequence; one might 
as well try to fit an extra integer between 7 and 8, or a new 
musicil note between F-sharp and G, (It is true that various 
extra elements have been made artificially in recent years, 
but these "lead on" from the end of the sequence, and probably 
do not occur naturally.) We can thus be certain that each 
Fraunhofer Line is due to an element or group of elements 
already known to us. 

When observed with the aid of a prism or spectroscope, 
the bright surface of the Sun, the photosphere, gives the bright 
rainbow studied by Newton. Above this is a layer of incandes- 
cent vapour, extending upwards for perhaps 10,000 miles. 
On its own, this vapour would give not a rainbow, but a 
number of bright isolated spectrum lines. However, there 
is the bright background to be taken into account, and the 
result is that instead of appearing bright, the lines emitted by 
the upper vapour are "reversed", and seem to be dark. This 
"reversing layer" is the outer envelope, or chromosphere.* 

The dark lines give us a key to the elements responsible 
for them. The spectra of the various elements have been studied 
in terrestrial laboratories, and the positions of the lines are 
known with high accuracy, so that all we have to do is to 
compare the laboratory lines with those visible in the solar 
spectrum. If a solar line corresponds to a laboratory line of 
sodium, we can prove that there is sodium in the Sun, In this 
way nearly 70 of the 92 familiar elements have already been 

We arc now in a position to examine the structure of the Sun 
itself. Near the centre of the globe, the pressure is tremendous, 
while the temperature is terrifyingly high — something like 
14 million degrees Centigrade, J which is beyond our compre- 
hension. It is here that the production of energy is going on, 

* Many books differentiate between the "reversing layer" and the "chromo- 
sphere", but there is no justification for this. The whole chromosphere is a reversing 
layer, though all the solar elements occur in the lower part of it, so that this part 
gives the most complete bright-line spectrum. 

t In general, I have given stellar temperatures in degrees Centigrade and 
planetary temperatures in Fahrenheit. Some may object to this practice, but it is 
very easy to convert one scale into the other. It involves nothing more frightening 
than simple multiplication and division. 



and the inner region has aptly been termed "the solar power- 

The visible surface of the Sun, the photosphere, is the 
region where the solar gases become thin enough to be trans- 
parent. The bright rainbow spectrum originates in the photo- 
sphere, and here too we meet the curious dark patches which 
are known, rather misleadingly, as sunspots. 

Above the photosphere we come to the chromosphere, or 
"colour sphere", made up largely of hydrogen gas. Except 
during a total solar eclipse, it cannot be seen except by using 
special instruments, since the intense glare from the photo- 
sphere hides it completely. Finally, beyond the chromosphere, 
we come to the extended outer atmosphere of the Sun, known 
as the corona. 

The most interesting objects in the chromosphere and 
corona are the prominences. These are masses of glowing 
vapour, composed mainly of hydrogen, helium and calcium. 
Some of them have been known to climb to a million miles 
above the bright surface, and they move so rapidly that there 
must be occasions upon which parts of them escape from the 
Sun altogether, leaking away into space. 

The difficulty of observing the prominences, the corona and 
other interesting high-level features is that the equipment 
needed is expensive to buy, and not too easy to make. The chief 
instruments of the serious research worker are the spectro- 
heliograph, the spectrohelioscope and the monochromatic 
filter, all of which enable the observer to study the Sun in the 
light of one particular element only — usually hydrogen or 
calcium. The prominences and the chromosphere may be 
studied at any time with such instruments, together with other 
features such as the dark patches known as flocculi or plages. 

Sunspots, which are almost equally interesting, can however 
be seen with any small telescope; some of them become 
large enough to be visible with the naked eye, and records 
of them go back to Ancient China. It is a fascinating pursuit to 
track them as they drift slowly across the Sun's disk, and to 
watch their shapes change from day to day. 

We have found out a great deal about the way in which 
sunspots behave, and wc also know that they are associated with 
magnetic phenomena. Broadly speaking, a spot may be 

b 65 


described as a relatively cool patch on the photosphere, so that 
it emits less light than the surrounding surface. "Cool", 
however, is here used in the solar and not the terrestrial sense ; 
the mildest part of a spot still has a temperature of some 
4,000 degrees, but the difference between this and the normal 
photosphere is enough to make the spot appear dark. If seen 
by itself, it would however glow with a brilliance much greater 
than that of an arc-lamp, so that it would be a grave mistake 
to describe a sunspot as "black". 

A large spot is made up of a relatively dark central pordon 
(umbra) and a lighter surrounding area {penumbra). Several 
umbrae may be contained in one mass of penumbra; sometimes 
the shape of the whole spot is circular, sometimes the outline 
is complex and irregular. Small spots may be made up entirely 
of umbra, while in complex groups the penumbral area is widely 

Spots may appear singly, but more often form groups. 
A common sight is to see two main spots, one lying to the 
west of the other, with numerous smaller ones near by. In 
general, the following or easterly spot is the first to decay and 
vanish. A really large group may contain dozens of separate 
umbrae, and sometimes the detail is so intricate that it is difficult 
to photograph and almost impossible to draw. 

The average spot lasts for about a week before it disappears, 
while smaller ones may have a lifetime of less than a day. 
Occasionally an unusually persistent spot makes its appearance; 
the record for longevity seems to belong to a spot which was 
seen from June to December 1 943, a total period of nearly 200 
days.* The spot was not, of course, under continuous observa- 
tion for the whole of that period. Since the Sun rotates on its 
axis, taking rather less than a month to do so, a spot group can 
be seen moving slowly across the disk as it is carried from east to 
west. The movement is too gradual to be noticed over short 
periods, but the shift from one day to the next is very obvious 
indeed. After a time, the spot will be carried over the 
western limb, and will not be seen again for a fortnight, after 
which it will reappear in the east — if, of course, it still exists. 

* The spot was followed by the late F. ,J. Sellers, formerly Director of the Solar 
Section of the British Astronomical Association, to whom I am indebted for 
this information. 



The numbers of sunspots vary in a semi-regular cycle. 
Maxima, during which spots are frequent, occur at intervals 
of about 1 1 years, with minima in between. During an active 
period there may be as many as a dozen groups visible at once, 
while near minimum the whole Sun may be spotless for weeks 
on end. This cycle was discovered by a German amateur, 
Hcinrich Schwabe, who drew the Sun on every possible day 
between 1825 and 1843, counting the observable spots and 
studying their individual characteristics. 

Actually, the cycle does not keep strictly to the 11 -year 
period. The interval between successive maxima may be as 
short as 9 years, or as long as 13I, so that no exact forecasts 
can be made; moreover, some maxima are more active than 

The maximum of 1947-48 was very energetic, and the great 
group of April 1947 was the largest ever seen; at the peak of its 
development it covered an area of over 7,000 milfion square 
miles. Minimum was reached in 1953-4, to De followed by 
another maximum in 1957-58. This was the period of the Inter- 
national Geophysical Year, a vast, world-wide co-operative 
programme involving scientists of more than fifty nations, and 
during which the Sun was intensively studied. There were 
large numbers of great spot-groups, some of them comparable 
with the giants of 1946 and 1947. 

Activity died away, as expected, and minimum was reached 
in 1964, when for a period there were few spot-groups. This 
lack of spots persisted until well into 1965. During this period 
another co-operative programme, the International Year of 
the Quiet Sun, was carried through successfully. During 1966, 
activity began to increase once more and maximum was 
reached in 1 969, though admittedly the level of activity was only 
about half that of 1957. The next maximum is due about 1980. 
Regular observation will show that the spots do not appear 
to move across the Sun in straight lines, except during early 
June and early December. This is because of the apparent 
shift in position of the Sun's axis of rotation. The position 
of the pole for any date can be looked up from the tables con- 
tained in a publication such as Tke Handbook of the British 
Astronomical Association, but the rough diagrams in Fig. 23 may 
be of help. . 



During the early part of a cycle, the spots tend to appear 
some way from the equator, but as the cycle progresses the 
spots invade lower and lower latitudes, As the cycle draws to 
its end, and its groups die away, small spots of the new cycle 
start to appear in high latitudes once more. At minimum, 
therefore, there are two areas subject to spots: the equatorial, 
with the last spots of the dying cycle, and the higher-latitude, 
with the first spots of the new cycle. This behaviour is termed 

Fig. 23. Apparent paths of sunspots. For the sake of clarity, the 
apparent shift of the Sun's pole of rotation has been exaggerated. 

Sporer's Law, since it was first announced in 1879 by the 
German astronomer of that name; it is extremely important to 
solar physicists. It should be added that spots never break out 
near the Sun's poles of rotation. 

Spots are associated with bright irregular patches known 
as faculje, from the Latin word meaning "torches". Facula: 
appear to lie well above the photosphere, and can be regarded 
as luminous clouds hanging in the upper regions. They often 
appear in positions where a spot -group is about to break out, 
and they persist for some time after the group has disappeared. 
Consequently, the appearance of facuke on the Sun's following 
limb is often an indication that a spot group is coming into 
view from the far side. 

Sunspots possess strong magnetic fields, and emissions from 
the active regions lead to disturbances of the compass needle, 
as well as to displays of aurone, or Polar Lights. It has also been 
suggested that sunspots affect the weather; the cold winters of 
I 9 I 6, 1927 and 1938 in Britain coincided roughly with maxima, 
while many people still remember the long "freeze-up" of 



j 04.7, when the Sun was so active; the minima of 1 92 1 and 1 932 
were accompanied by droughts. Nowadays, however, the 
connection between spots and the weather is regarded as 
distinctly dubious. The bitter weather in Britain during early 
j 063 coincided with an approaching solar minimum, so that 
at best the correlation is unreliable. 

Even on the unspotted parts of the Sun, a certain amount of 
activity is always going on. The photosphere is not at peace; 
it is covered with "granulations", which are in a state of con- 
stant turbulence, and seldom last for long. Generally, a granule 
has a width of something like 500 miles. The nature of the 
granules is not definitely known, but the granular structure 
may well be due to the tops of gas-currents which rise and fall. 

Very occasionally, brilliant short-lived patches may be seen 
over sunspots. The first of these "flares" was seen in 1859 by 
two amateurs, Garrington and Hodgson, but for many years 
no more were recorded. Flares visible in ordinary telescopes 
are in fact so rare that an observer may go through his whole 
lifetime without seeing one, but modern instruments have 
shown that the solar flare is a common phenomenon. 

Flares are, naturally, commonest near the times of solar 
maxima. They may be described as being storms in the 
chromosphere, of an electrical nature, the hydrogen atoms 
being caused to glow brilliantiy by electrical excitation. They 
spread through large areas of the chromosphere horizontally, 
i.e. parallel with the solar surface, with amazing rapidity, but 
there is very litde vertical movement; they seem to be confined 
to the 8,000 or 10,000 miles of the chromospheric depth. They 
produce marked effects upon the terrestrial compass-needle, as 
well as helping to cause radio fade-outs and other disturb- 

Features of the upper layers, such as prominences, are best 
discussed together with eclipses of the Sun, and it will be wise 
to restrict the present chapter to objects which can be seen with 
ordinary telescopes. 

Observing the Sun is not the simple matter that might be 
imagined. Even a small telescope can concentrate so much light 
and heat that an incautious observer who puts his eye to the 
tube may be blinded. Very great care is necessary at all times; 
it is only too easy to make a mistake. 



^ Unfortunately, it is possible to buy special dark-lensed 
"suncaps" which fit over an ordinary eyepiece, and can be 
used for direct observation. According to some textbooks, it is 
then safe to turn a 2- or 3-inch refractor directly towards the 
Sun, and observe in the usual manner. This is emphatically not 
the case. No suncap can give full protection, and in any case 
there is always a chance that the cap will splinter, so that the 
eye of the observer will be seriously injured before he has had 
time to realize what has happened. This warning is not mere 
alarmism; I know of one amateur who lost the sight of his left 
eye through an accident of this sort, and the risk is not worth 
taking, particularly when better observations can be made by 
indirect means. 

There is another danger also. Sometimes the Sun can 
be seen shining through a layer of thick mist, so that it appears 
reassuringly dim and gentle. The temptation is then to use a 
telescope directly, either with or without suncap. Here again 
there is more than a chance that permanent damage to the eye 
will result; as soon as the solar radiation is focused, it becomes 
unsafe. In short, never look straight at the Sun even with 
binoculars. It is true that some kinds of special eyepieces, known 
as wedges, are fairly harmless; but the only really sensible way 
to draw sunspots is by projecting them on to a piece of 
white card. 

Projection is an easy process, since there is plenty of light 
available. First turn the telescope in the direction of the Sun, 
"squinting" over the top of the tube and keeping a cover over 
the object-glass. Then rack out the focus, and remove the cap 
from the end of the tube. Hold a white card a few inches away 
from the eyepiece, and move the telescope gently (if necessary) 
until the image of the Sun appears, after which the disk can be 
brought to a sharp focus by adjusting the rack and the position 
of the card (Fig. 24). Any spots and faculse that happen to be 
present will be obvious at a glance. A low power is advisable— 
I have found that for my 3-inch f/12 refractor, x 72 gives good 
results — though the magnification can be increased for draw- 
ings of individual spots on a larger scale. 

To make the drawings conveniently standard, it is as 
well to draw a 6-inch circle on a card and then adjust the 
distance and focus until the image of the Sun exactly fills it. 



If the telescope used is very small, a 4-inch circle may have to 

It is not easy to hold the card steady, move the telescope to 
follow the Sun, and draw the visible spot-groups at the same 
time. One would have to be a Briarseus to do so effectively, and 
the obvious solution is to fit an attachment to the telescope 
tube which will hold the card at the right distance from the 
eyepiece. Such an attachment can be built by anyone who is 
reasonably skilful with his hands, and there is nothing in the 
least difficult about it. The main thing to avoid is upsetting the 
balance of the telescope tube. 

Fig, 24. Simple projection of sunspots, using a 3-in. refractor. 

When the drawing has been finished, the following details 
should be added: date, time (G.M.T.: never Summer Time), 
observer's name, aperture of telescope, and magnification. If 
any of tliis information is omitted, the drawing promptly loses 
most or all of its value. 

In general, refractors are to be preferred to reflectors for 
solar work, and the ideal aperture is from 4 to 5 inches. A 
6-inch is larger than is necessary, and extra care must be taken. 
In the case of a reflector, the mirror should be left unsilvered, 
which naturally makes the instrument almost useless for any 
other kind of work. During the many years that I have owned 
my 12^-inch reflector, I have never turned it towards the Sun, 
and nor shall I ever do so. My portable 3 -inch refractor will 



show the spots and faculse quite well enough, and to use a 
large telescope in such a way would be madness. 

Spots and faculae may, of course, be photographed, and 
no really elaborate equipment is required. Excellent results 
may be obtained with a modest 3-inch refractor. Outstanding 
photographs were regularly secured by the late W. M. Baxter, 
using the 4-inch refractor at his observatory in Acton; some of 
these are reproduced on Plate III, and their quality is obvious. 

Such work is decidedly useful. In particular, Baxter carefully 
investigated the so-called Wilson Effect. If a sunspot has 
a depressed umbra, the "preceding" penumbra will be fore- 
shortened, and will appear narrow as the spot comes over the 
limb, while when the spot has crossed the disk and is approach- 
ing the opposite limb the "front" penumbra will appear to be 
the broader. In fact, with a circular sunspot which has a 
depressed umbra, the penumbra closest to the Sun's centre 
will always seem to be narrower than that on the opposite 
side of the spot. Baxter found that the Wilson Effect is often 
perceptible, so that most sunspots are relatively shallow 
hollows a few hundred miles deep, but now and then he has 
studied an unusual spot where the Effect is actually reversed. 
More research is needed, and amateurs can do valuable work 
both visually and photographically. 

The amateur who is prepared to buy or build a special 
instrument, such as a spectrohehoscope, will have almost 
unlimited scope in the field of solar observation. Even a simple 
spectroscope will show the prominences, and this at least is 
within the powers of any skilful amateur, as can be seen by 
reference to the books listed in the Appendix. A Lyot mono- 
chromatic filter is even more convenient. 

While it would be idle to pretend that the observer who 
contents himself with drawing sunspots with the aid of a small 
refractor has much chance of making a valuable discovery, 
particularly since daily disk photographs are taken at solar 
observatories, the time spent will not be wasted. Much will 
be learned; it is fascinating to watch the spots and faculas 
as they drift, change and finally die away. Yet we must never 
forget that we are unworthy to take liberties with the ruler 
of the Solar System. A cat may look directly at a king, but no 
telescopic worker must ever look directly at the Sun. 


Chapter Six 


The moon is much the closest natural body in the sky. On 
average it is a mere 239,000 miles away from us; and although 
it is smaller than the Earth, with a diameter of only 2,160 miles, 
it dominates the scene during the hours of darkness. It is hardly 
surprising that our ancestors worshipped it as a god. 

Definite markings can be seen with the naked eye, and any 
telescope or pair of binoculars will show a vast amount of detail. 
There are mountains, valleys and craters ; the sight of a lunar 
landscape is something never to be forgotten, and the Moon 
will always be the favourite object for amateur observation. 
Moreover, amateurs have Carried out very useful work in lunar 
charting. It is probably true to say that before the start of the 
Space Age, the best of all Moon-maps were of amateur con- 

The situation today is very different. The Moon is no longer 
inaccessible ; it has been reached, and many of its outstanding 
problems have been cleared up, though many more remain to 
be solved. Quite apart from the manned landings, there have 
been automatic probes which have flown round and round the 
Moon, securing photographs of amazing detail and quality, so 
that by now we have extremely accurate charts of the entire 

In astronomy, as in everything else, honesty is the best policy, 
and it is best to admit immediately that in most ways, though 
not all, the amateur lunar observer has completed Ills task. 
There is now no scientific value in, say, making a chart of a 
limb area with the aid of a 6-inch or even a 1 2-inch telescope. 
It is still worth doing, for the pleasure that it gives the observer ; 
but modern lunar mapping is carried out from beyond the 
Earth. Only in a few restricted fields is original lunar research 
still within the scope of the amateur. The last thing I want to do 
is to be discouraging— and, as a personal aside, I have always 
been more concerned with observation of the Moon than with 




any other branch of astronomy. But there is no point in not 
facing facts. 

Before going into the story of how the Moon has been 
explored, it may be best to give a brief description of the lunar 
world itself. It is usually called the Earth's satellite, but in my 
view, at least, this is misleading; it is too large to be a satellite. 
Remember, its diameter is more than one-quarter of that of the 
Earth (Fig. 25), and there now seems no doubt that it has 

always been a separate body; 
the old theory according to 
which it used to be part of the 
Earth, and was thrown off 

©into space, has been rejected 
on mathematical grounds. 
Either it used to be an in- 
dependent planet which was 
captured by the Earth in the 
Fig. 25. Comparative sizes of remote past, or eke (more 
the Earth and Moon. probably) it and the Earth 

were formed in the same 
region of space at about the same time, so that they have 
always been associated. It is best to regard the Earth-Moon 
systems as a double planet. Rock specimens brought back from 
the Moon by the space probes confirm that the ages of the two 
worlds are about the same (around 4,700 million years). 

It is not stricdy true to say that the Moon moves round the 
Earth; more accurately, both bodies move round the barycentre, 
or centre of gravity of the system. However, the barycentre 
lies within the Earth's globe, since the Earth is so much more 
massive than the Moon; the ratio is 8 1 to 1 . The Moon is the main 
force in the raising of the tides. In this respect it is much more 
effective than the Sun, simply because it is so much closer to us. 
The Moon's low mass means that it has also a low escape 
velocity: i\ miles per second, instead of 7 miles per second as 
for Earth. In its younger period it may have had an atmosphere, 
but the weak gravity has meant that virtually all this atmos- 
phere has escaped into space. Nowadays the Moon is "airless", 
and careful measurements carried out by Apollo astronauts on 
the actual surface have proved to be entirely negative. From the 
Moon, the sky appears black even when the Sun is above the 



horizon. It used to be thought that stars would be visible in 
broad daylight, though Neil Armstrong, the first man to set foot 
on the lunar surface, has told me that neither he nor his com- 
panion, Colonel Edwin Aldrin, observed any stars during their 
"moon-walk", because of the glare from the surrounding 
landscape. All the odier Apollo astronauts found the same 


The Moon is a slow spinner. Its rotation period is 27-3 days, 
which is the same as the 
time taken for the Moon to 
go once round the Earth (or, 
properly speaking, around 
the barycentre). The effect 
of this synchronous or 
"captured" rotation is that 
the Moon keeps the same 
face turned toward us all 
the time. This sometimes 
causes confusion, but a 
simple experiment will 
show what is meant. Place 
a chair in the middle of the 
room, to represent the 
Earth, and assume that your 
head is the Moon. Your face 

stands for the familiar hemisphere, while the back of your neck 
represents the "back" of the Moon (Fig. 26). Now walk round 
the chair, keeping your nose turned toward it all the time. When 
you have completed one circuit, you will have turned round 
once; your "sidereal period" will have been equal to your 
"axial rotation", and anyone sitting on the chair will not have 
seen your back hair at all. This is how the Moon behaves. Just 
as the seated observer failed to see the back of your neck, so 
the terrestrial observer can never see the far side of the Moon. 

However, there is one modification. Though the Moon spins 
on its axis at a constant speed, it has a somewhat eccentric 
orbit, and this means that its velocity varies. When at its closest 
to the Earth, it moves quicker than when more distant. The 
axial spin and the position in orbit become periodically out of 
step, and the Moon seems to rock slowly to and fro, allowing us 


Fig. 26. A simple demonstration 

of the movement of the Moon 

round the earth. 


to view first one limb and then the other. On some nights, the 
grey plain of the Mare Crisium (Plate IVc) will appear to be 
almost touching the limb, while on others it will be well clear, 
and more details will come into view. There is also a rocking in 
a north-south direction, since the Moon's orbit is tilted, and we 
can peer for some distance beyond alternate poles. These 
rocking motions or "librations" mean that from Earth we can 
examine a total of 59 per cent, of the total surface, though, of 
course, never more than 50 per cent, at any one time. The 
remaining 41 per cent, is always out of view. Until the first 
circum-lunar rocket sent back photographs, in 1959, we had no 
positive information about "the other side of the Moon". 

There is one more point to be borne in mind. The Moon 
always keeps more or less the same face turned to the Earth, but 
it does not keep the same face turned toward the Sun, so tiiat 
day and night conditions arc the same everywhere on the 
Moon's surface; it is quite wrong to suggest that there is a part of 
the Moon which is always dark. The only real difference is that 
from the far side, the Earth will never be seen, so that the nights 
will be blacker due to the absence of Earthlight. 

Of the lunar features, the most immediately obvious are die 
dark grey plains which are always known as seas (Latin, maria). 
They were first charted telescopically by Harriott in 1609, and 
shortly afterwards a map was produced by Galileo. It was 
natural to suppose that the plains were water-filled, even though 
Galileo himself apparently had doubts; and the romantic names 
are still used, even though we have long since found that there 
is do water on the Moon. One cannot have liquid water in the 
absence of atmosphere; and analyses of the Apollo samples 
seem to prove that the lunar seas were never water-filled. 

Many of the seas, such as the vast Marc Imbrium* (Plate 
XVI between pages 226-7) are roughly circular in form. Their 
boundaries are raised, and form mountain chains, some of 
which are high by our standards. For instance, the Lunar 
Apennines, which form part of the border of the Mare Imbrium, 
have peaks rising to 15,000 feet. Other parts of the border are 
formed by the Alps, cut through by a magnificent valley, and 
the Caucasus Mountains, which separate the Marc Imbrium 

* I 1 seems best lo beep to the Latin names, which arc always used in astrono- 
mical literature. A full list of these, together with their English equivalents, is 
given in Appendix XH. 



from the neighbouring plain. Earth-type mountain chains are 
rare, but isolated peaks and clusters of hills are almost innumer- 
able. The very highest mountains on the Moon exceed 25,000 
feet. Their altitudes are measured by the shadows which they 
cast, though the situation is complicated by the fact diat on the 
waterless Moon there is no sea-level to serve as a standard for 
reference. Formerly, amateurs carried out valuable work in this 
direction, though we must concede that space-research methods 
have now taken over. 

The whole scene is dominated by the walled circular forma- 
tions which we usually call craters. No part of the Moon is free 
from them. They cluster in the bright uplands, and are also to 
be found on the maria, on the slopes of mountains and even on 
the crests of the peaks. They break into each other and deform 
each otiier; some have massive, terraced walls and high central 
mountain structures, while others are low-walled and ruined, so 
that they come into the category of "ghosts". The very largest 
of them exceed 150 miles in diameter. The smallest are too 
minute to be seen at all from Earth. In general, they are named 
after famous personalities of the past. Features on the far side of 
the Moon, invisible from Earth, have also been named. A full 
list was approved by the International Astronomical Union 
during its meeting in England in the summer of 1970. 

Though some of the craters are deep, with walls rising to well 
over 10,000 feet above the floors, they are not in the least like 
steep-sided mine-shafts. A typical large crater has a mountain 
rampart which rises to only a moderate height above the outer 
country, but much higher over the sunken interior. The inner 
walls are often terraced, so that a lunar crater has a profile more 
like that of a saucer than a well. This is shown in Fig. 27, in 
which the famous 38-mile crater Eratosthenes is drawn. Like 
many other walled formations, Eratosthenes has a central 
elevation which may look inconspicuous, but which is really 
lofty. With some craters, the central structure is a single peak; 
inside other formations we see clusters of hills, while central 
craterlets are also frequent. On the other hand, there are also 
formations whose floors are flatter, and which have no central 
structures. The dark-floored, 60-mile Plato is an example of 
this (Plate XVI). Like most of its kind, Plato is circular; but as 
seen from Earth it seems oval, because of foreshortening. Photo- 



graphs of it taken "from above", by lunar probes of the Orbiter 
variety, show it in its true guise. 

How were the craters formed ? This is a problem which has 
caused an immense amount of argument — some of which has 
been strangely acrimonious. It had been widely supposed that 
the first manned landings would provide a definite answer, but 
so far this has not happened, and the arguments continue. 
Various weird and wonderful theories have been proposed, but, 
basically, the controversy centres around whedier the craters 
were produced by internal action (that is to say, volcanic 
activity in some form or other) or by external bombardment 

Fig. 37. Cross-section of the lunar crater Eratosthenes. The diagram 

is simplified for the sake of clarity ; the curvature of the lunar surface 

b neglected, and the central elevation is shown as a simple peak 

instead of a complex mass. 

(that is to say meteoritic impact) . No doubt both kinds of craters 
exist on the Moon, just as on Earth, and the point to be decided 
is which process played the more important r61e. My own view 
is, and always has been, that most of the major craters are due 
to internal forces. Random bombardment would have produced 
a random crater distribution, and this is emphatically not the 
case, either for the large features or for many of the smaller 
ones. Nothing that the lunar probes have told us so far has 
caused me to change my opinion ; but the last word has by no 
means been said, and there seems no point in delving more 
deeply into matters here. Note, however, that the rock samples 
obtained from the lunar surface are made up of typically vol- 
canic material, and that no meteorites have yet been found on 
the surface of the Moon. 

Of the minor features of the Moon, special mention must be 
made of the clefts or rills, which look like surface cracks and 
which extend in some cases for over too miles. An excellent 



example is the long cleft associated with the crater Ariadaeus, 
shown on the map in the Appendix (page 226). Close beside it 
is another so-called cleft, that of Hyginus, which is made up 
partly of small craterlets. Look, too, at the magnificent cleft 
inside the majestic ringed plain Petavius, running from near the 
central mountain across to the wall. Over the whole of the 
Earth-turned face, there are many clefts and cleft-systems 
within range of modest telescopes. 

Quite different are the domes, which may be likened to 
gentle swellings in die crust; many of them have summit crater- 
lets, and some are riddled with fissures. And, of course, there are 
the bright rays which spread out from some of the prominent 
craters. Tycho, in the southern uplands, is the centre of a ray- 
system which extends in all directions for hundreds of miles, 
while another major centre is Copernicus in the Mare Nubium. 
The rays are surface deposits, and best seen only under high 
illumination — a point to which I will return presently. 

Very few professional astronomers paid much attention to the 
lunar surface before the igsos. Then, however, it became clear 
that the Moon was within reach, and there was a prompt 
upsurge of professional activity. Most of the groundwork had 
been carried out by amateurs, who had performed nobly, and 
there were various maps which were of liigh accuracy by the 
prc-Space Age standards. The next step was to undertake a full 
photographic survey, and work was begun in various countries, 
notably the United States. Detailed photographic atlases 
appeared, superseding the older visual charts. 

Then, in 1959, came the first Moon-rockets. The first three 
were Russian; Lunik I, which by-passed the Moon, was the 
pioneer vehicle in January. It was followed by Lunik II, which 
crash-landed on the surface, and then, in October, by Lunik III, 
which went round the Moon and sent back the first photographs 
of die far side. Today, the Lunik III pictures look very blurred, 
but that they were an immense technical triumph cannot be 

The next step was taken by the Americans, with their Ranger 
programme. The scheme was to crash a probe on to the Moon 
without any attempt to preserve it. Before impact, it would 
send back close-range television pictures. There were several 
failures, but success came on July 31, 1964, with Ranger VII, 



which came down in the Mare Nubium. The photographs were 
excellent, as were those from the succeeding Rangers, Numbers 
VIII and IX. Ranger IX was aimed at the large crater 
Alphonsus, in which a certain amount of volcanic activity had 
long been suspected. 

The year 1966 was important in lunar research. First there 
was Luna 9, a Russian triumph. The vehicle landed on the 
Moon, in the Ocean us Procellarum, but did not destroy itself 
as the Rangers had done; it came down gently, so that after 
arrival it was able to go on transmitting information. The 
pictures it sent back were the first to be obtained direct from the 
surface of another world, and they showed a terrain which 
looked remarkably like a lava-field. 

The second important development of 1 966 was an American 
success. On August 1 o, Orbiter I was launched, and put into a 
path round the Moon, Photographs were received from both it 
and its four successors, and at once all Earth-based charts were 
made obsolete. There is still much work to be done in analysing 
the many thousands of Orbiter photographs, which show the 
Moon in remarkable detail. By August 1967, when Orbiter V 
was launched, the programme was more or less complete. 

Of course, all these experiments were leading up to the 
greatest project of all : Man on the Moon. So many accounts of 
the Apollo programme have been published that there seems no 
point in saying a great deal about it here, but I must make some 
comments, because they arc important in my present context. 

On July 21, 1969, Neil Armstrong and Colonel Edwin Aldrin 
in Apollo 1 1 achieved the first landing. They came down in the 
Mare Tranquillitatis, not far from the small but well-marked 
crater Moltke. The whole expedition was watched by television 
viewers all over the world, and it was something that will never 
be forgotten. Then, in the following November, Charles Conrad 
and Alan Bean in Apollo 1 2 made a second landing, this time 
not far from the crater Landsberg (Plate XVIb). Both expedi- 
tions brought back samples of lunar material, which proved to 
be of volcanic type, and which contained countless small glassy 
particles often called "marbles". The rocks of the Moon are 
very old indeed; as expected, there was no sign of any fife either 
past or present, and neither was there any indication that the 
lunar seas had ever been watery. 



Apollo 13, of 1970, will also be remembered — but for a 
different reason. Everything went wrong. During the outward 
journey there was a violent explosion, which robbed the space- 
craft of its main power sources. The lunar landing, scheduled 
for the upland area of Fra Mauro (Plate XVIb) was abandoned, 
and it was only by a combination of brilliant improvisation, 
courage and skill that the astronauts returned unscathed. 

The last three Apollo missions were undoubtedly die most 
valuable scientificially. On each trip the astronauts took their 
own transport, and the "Moon Rovers" functioned admirably. 
The Apollo programme ended in 1972 with No. 17, and it was 
then that Dr. Harrison Schmitt, a geologist who had qualified 
as an astronaut, made the discovery of "orange soil" near a 
small crater which had been nicknamed Shorty. Yet the orange 
colour did not indicate recent vulcanism, as had been thought 
at first; it was due to large numbers of small orange-coloured 
pieces of glass. Moreover, it was very old. Just why it was so 
localized remains a mystery. 

Quite clearly the Apollo missions have increased our know- 
ledge of the Moon beyond all recognition. Neither have the 
Russians been idle; in 1970 they sent up the first automatic 
probe which collected lunar samples and returned home, and 
later in the same year they dispatched Luna 17, which was 
even more spectacular. From it crawled Lunokhod i, which 
looked like a cross between a surrealistic saucepan and an 
ancient steam-car, but which explored the whole area with 
amazing efficiency. Lunokhod 2 was equally successful. With 
all this "space activity", we are bound to ask ourselves: What 
can the amateur observer still usefully do? 

Analysis of Orbiter photographs is valuable, and as time goes 
by more and more of these photographs are being released and 
made available, but telescopic work is still useful in one way. 
What the serious amateur must now do is to concentrate upon 
what may be termed time-dependent phenomena. The Moon is 
not an active world, and it always looks much the same; but 
tiny changes and traces of activity do occur, and it is here that 
the amateur comes into his own. 

However, great care is needed, and the essential first step is to 
learn one's way around. It is hopeless to start any systematic 
programme until all the main features, and many of the minor 

, 81 


ones, can be recognized on sight. Crater identification is not so 
difficult as it may seem, but various basic points have to be 
bome in mind. When a crater is near the terminator, or bound- 
ary between the daylight and night hemispheres of the Moon 
(Fig. 28), it wili have shadow inside it, and will be strikingly 
conspicuous; under higher illumination, the shadows will 
shrink, and the crater may become hard to find. Toward fidl 
moon the shadows almost disappear, and even large craters are 
difficult to locate unless they have particularly bright walls 
(such as Aristarchus) , particularly dark floors (such as Plato) or 
ray systems (such as Tycho). It is therefore wrong to suppose 
that full moon is the best time to start observing; on the con- 
trary, it is the worst, except for special investigations, particu- 
larly as the bright rays dominate the scene completely. The 
most spectacular views are obtained during the crescent, half 
and moderately gibbous stages. 

I can cite a personal 
experience here. I first 
looked at the Moon 
through a telescope when 
I was a boy of eight, and 
since I knew no better 
I decided to make a start 
on the night of full moon. 
I looked up the position of 
the 92-mile crater Ptole- 
mecus, arranged my newly 
acquired 3-inch refractor, 
and tried to find my way 
about. Naturally, I failed 
to find Ptolemseus. When 
I looked again at the time 
of half-moon, the crater 
was partly filled with 
shadow, and I could 
identify it at first glance. 
The method I then adopted — and which I still recommend — 
was to obtain an outline chart of the Moon and then set out to 
make at least two sketches of every named feature. The pro- 
cedure takes a long time, because a normal crater can be well 


Fig. 28. Limb and terminator. The 

limb is drawn as a continuous line, 

while the terminator is dotted. 



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Fig. 29. Section from the author's 2-foot map of the Moon. 



sketched only when there is some shadow inside it and one has 
to make the most of one's opportunities. By the time I had 
finished it had taken me more than a year. The sketches them- 
selves were useless, as I knew they would be; but at least I 
had learned how to tell one crater from another. The map I 
used was Elger's, published in 1896. Since then (1969) I 
have drawn a slightly larger outline map, though it too makes 
no pretence of being anything more than a guide (Figs, 29 
and 30). 

It is a great mistake to make a drawing too small, or to 
attempt too large an area at one time. Probably about 20 miles 




<s. ^littitei^H 

Fig. 30. Th 

hus area, from the author's 2-foot lunar map. 

to the inch is a good scale. "Finished" drawings look attractive, 
but an observer with no artistic gifts, such as myself, may be 
wiser to keep to line drawings. Accuracy is always the main 
objective. Always remember that a crater alters in appearance 
according to illumination, so that it is necessary to identify it 
under all possible conditions of fighting. 

Incidentally, some recent decisions have caused a good deal 
of confusion. "East" and "west" have always been standardized 
so that, for instance, Mare Crisium is near the west limb. The 
American space authorities have reversed this, making east 
west and west east; they also put north at the top. In the present 
book I have followed the American east-west practice, because 



it has been accepted by the Lunar Commission of the Inter- 
national Astronomical Union. (Only a few rebels, such as my- 
self, voted against it!) However, I have kept south at the top, as 
has always been customary. 

It used to be officially laid down that the Moon is entirely 
changeless. Admittedly there was one alleged case of alteration 

m the formation Linn6, on the Mare Sercnitatis, which was 

drawn as a crater by all observers before 1843, and since 1866 
has been a small craterlet surrounded by a white patch— but 
the evidence was most incomplete, and the other reported 
instances were even more uncertain. It seems that large-scale 
alterations on the Moon belong to the remote past. Yet in 
recent years there have been observations of a different kind, 
involving temporary reddish patches. These are known as 
Transient Lunar Phenomena, or, for short, T.L.P-s. 

The story of T.L.P.s goes back a long way. Amateurs recorded 
the patches now and then, but their reports were regarded with 
some scepticism, because none could be photographically con- 
firmed. In fact, this scepticism was unwise; before about 1950 
the only observers who were paying systematic attention to the 
Moon were of amateur status, and it is true to say that in this 
field, at least, their opinions should have carried great weight. 
Then, in November 1958, the Russian professional astronomer 
N. A. Kozyrev, using the 50-inch reflector at the Crimean 
Astrophysical Observatory, recorded temporary red colour 
inside the large crater Alphonsus (Plate XVI b) and confirmed it 
spectrographically. He attributed it to gaseous emission from 
below the crust, due to weak vulcanism. Though this interpre- 
tation could be questioned, the validity of the observation 
itself could not — and was not, except by a few extremists. In 
1963 observers at the Lowell Observatory, in Arizona, saw 
some more red patches, tliis time in the area of Aristarchus, the 
most brilliant crater on the Earth-turned hemisphere of the 
Moon. There was ample confirmation, and it became clear 
that the amateur reports had been jettisoned much too hastily. 
On April 30, 1966, the British amateur P. K. Sartory, from 
his observatory in Surrey, detected redness close to Gassendi, a 
large crater on the border of the Mare Humorum. The Lunar 
Section of the British Astronomical Association, of which I was 
then Director, had established an organization to study this 



sort of phenomenon, and the Gassendi patches were confirmed 
by independent observers — by P. Ringsdore in Ewell and by 
T. Moseley and myself at Armagh. We did not compare notes 
until later, and the agreement was so good that no reasonable 
doubt can remain. 

Meantime, Miss Barbara Middlehurst, at the Lunar and 
Planetary Laboratory at Tucson, Arizona, had been collecting 
past reports of T.L.P. phenomena. There were plenty of them; 
some areas, such as Aristarchus, were particularly prone to 
them, and there seemed to be a definite periodicity about them, 
connected with the Moon's changing distance from the Earth. 
I had been carrying out a similar investigation, and when we 
compared our results they were strikingly similar, so that they 
were published as a joint paper. In 1970, results obtained from 
the seismometer left on the Moon by astronauts of Apollo XII, 
gave striking confirmation. Moonquakes do occur; they are 
linked with the Moon's changing distance, inasmuch as they 
are commonest at the time of perigee, and they are linked too, 
with the T.L.P.S. Dozens of reliable cases of T.L.P.s are now on 
record. During the Apollo flights, lunar observers — both pro- 
fessional and amateur — have been officially requested to keep a 
systematic watch for the strange red glows, and to report any 
results to a special committee set up by the American space 
Agency, NASA (National Aeronautics and Space Administra- 

There is considerable disagreement about the origin of 
T.L.P.s, though the original theory of gaseous emissions has— 
in my view — much to recommend it. However, the main need 
at the moment is to continue with systematic observation. It 
may be that the phenomena occur in cycles, with an active 
spell followed by a prolonged lull. 

Many of the observations are carried out with a device known 
as a Moon-Blink. This takes the form of a rotating wheel, with 
red and blue colour filters, placed just on the object-glass side of 
the eyepiece (or the mirror side, with a reflector). A red patch 
on the Moon will show up as a dark feature when observed 
through a blue filter, but will be masked with a red filter. 
Rotating the wheel, one observes first through the red, then 
through the blue filter in quick succession, so that any red patch 
will show up as a "blinking spot". The method is sensitive, 



and phenomena can be detected which could otherwise be 
missed, though naturally it is confined to red events. 

It is not hard to make a Moon-Blink device, and it can be 
used with a modest telescope, though I would not be happy 
with anything smaller than an 8-inch. Yet here, above all, it is 
vital to avoid jumping to conclusions. It is only too easy to "see" 
what one half-expects to see, and a bad observation is worse 
than useless; it is actively misleading. In the final analysis, it is 
essential to deal only with reports from observers who are both 
experienced and adequately-equipped. 

In T.L.P. work, ordinary photography can hardly be used ; 
but there is immense enjoyment to be gained from taking lunar 
pictures, and the results can be remarkably good. For instance, 
a full photographic atlas was published some years ago by 
Commander H. R. Hatfield, a British amateur who has built 
his own 12-inch reflector and his own camera. Nobody, least of 
all Commander Hatfield, would claim that the results can rival 
Orbiter; but they stand up very well to photographs taken from 
Earth-based observatories with much larger and more elaborate 
telescopes. Remember, however, that for lunar photography a 
clock-driven telescope is needed. Anyone who holds up a 
camera to an unguided telescope and "clicks" hopefully is 
doomed to disappointment. 

Everything we have found out since the beginning of the 
Space Age stresses the unfriendly nature of the Moon. It lacks 
atmosphere and water; its temperatures arc extreme, ranging 
from above 200 degrees F. at the equator during daytime to 
below - 250 degrees F. at night; there is no life there, and we 
may now be sure that the Moon has been sterile throughout its 
history. Yet it remains of supreme importance to us, and the 
time cannot be far distant when a full-scale scientific base will 
be erected there. 

Even when this has happened, the Moon will retain its 
fascination to those of us who can never hope to travel in space. 
It is unique; it can never lose its appeal or its romance. There 
will always be endless pleasure to be gained from turning a 
telescope toward it and looking at the craters, the mountains 
and the valleys, learning how to recognize them and watching 
their shadows shift and change as the Sun rises over them. 


Oiapter Seven 


So far as the Solar System is concerned, there are long 
periods in which the observer has to content himself with 
purely routine work. This may well be followed by a number of 
interesting phenomena which occur in quick succession. There 
is perhaps a violent outbreak of sunspots, or a favourable 
opposition of Mars; a bright comet may make a dramatic and 
unexpected appearance. Also to be considered are occultations 
and eclipses, which have been described as the celestial equival- 
ents of hide-and-seek. 

The Moon is much the closest body in the sky, and so moves 
across the starry background at a relatively high speed. Some- 
times it must, of course, pass in front of a star and hide it. 
These "occultations" are common enough, but are not so 
numerous as might be thought. People tend to over-estimate 
the size of the Moon in the heavens, and artists will usually 
draw it as large as a dinner-plate, whereas the apparent 
diameter is actually the size of an old halfpenny (i inch) held 
9 feet away from the eye. 

Consequently, the Moon does not pass in front of several 
stars per hour. During 1967, for instance, as seen from Britain 
there were no occultations of stars bright enough to be shown 
in the star-maps in the Appendix. The Moon, like all the 
planets, keeps to the Zodiac, so that only stars close to the 
ecliptic can be occulted; the brightest of these are Antares, 
Aldebaran, Spica and Regulus. Occultations of planets can 
also occur at times. 

A planet shows a definite disk, so that it takes some seconds 
for the oncoming limb of the Moon to pass right over it. A star, 
however, appears as a tiny point of light, and the disappearance 
is virtually instantaneous. The star shines steadily until the 
moment of occultation, and then seems to snap out like a 
candle-flame in the wind. One moment it is there, the next it has 



gone. This is one proof that the Moon has little or no atmos- 
phere, since a blanket of air around the limb would make the 
star flicker and fade for some seconds before vanishing. 

Seen in a telescope, an occultation is a fascinating sight. The 
star seems to creep up to the Moon's limb, though actually the 
Moon's own motion is responsible, and the inexperienced 
observer is bound to feel that the star hangs close to the limb 
for a long time. Then the brilliant point of light will "softly 
and suddenly vanish away", like the hunter of the Snark, and 
a watcher who blinks his eyes at the wrong moment may easily 
miss the disappearance. The emersion, at the far limb, is equally 

Occultations are more important than one might think. 
They can be predicted, and The Handbook of the British Astro- 
nomical Association gives a list for each year, but the predictions 
may not be absolutely correct, owing to the fact that the 
Moon's apparent path in the sky is not known with com- 
plete precision. The star positions are much more certain, and 
so an occultation enables astronomers to correct their lunar 
tables. If the disappearance is timed accurately, it gives the 
actual position of the Moon's limb at that moment. 

This is work that the amateur can do, but, like all other 
observations, it must be carried out with extreme care. I 
once had a report from an observer who said that the star 
Omega Leonis "was occulted at about twenty minutes past 
ten". This sort of thing is useless. The occultation must be 
dmed to an accuracy well within one second of time if it 
is to be of any value whatsoever. A really good stop-watch is 

When an occultation report is drawn up, the following data 
should be added: name or number of star, time of occultation, 
latitude and longitude of observing station, height above mean 
sea level of observing station, atmospheric conditions, and any 
peculiar appearance seen. Occasionally, a star is hidden by a 
lunar peak on the limb and then reappears briefly in the 
adjacent valley before vanishing once more, so that it seems to 
wink. This cannot be predicted, since we do not know either 
the position of the Moon or the contour of the limb with 
sufficient accuracy. 

Now and then, unexpected occultations take place — 



unexpected in the sense that they are not listed in the available 
tables. During one lunar eclipse, I witnessed an occultation of 
the planet Uranus that I certainly did not anticipate. The 
tables at my disposal made no mention of it, though the occulta- 
tion was of course known to those who had made calculations 

Patience and practice are vital in all occultation work, but 
the time taken will be amply repaid by the fact that valuable 
observations can be made. A small telescope will prove perfectly 
suitable, and can well be mounted on an altazimuth provided 
that the stand is steady. 

Planets, too, can occult stars. The most valuable of the plane- 
tary occupations are those due to Venus, because the flickering 
and fading of the star before disappearance gives a clue as to 
the height of the atmosphere surrounding that mysterious 
world. On July 7, 1959, for instance, Venus occulted Regulus; 
the phenomenon took place in the early afternoon, and observa- 
tions made by Henry Brinton and myself, using Brinton's 
ia|-inch reflector, showed a perceptible dimming lasting for 
almost one second. Unfortunately, occultations by planets are 
comparatively rare, but they are very well worth observing. 

It should be added that there have been cases of one planet 
hiding another; for instance, Venus occulted Mars in 1590 
and Mercury in 1737. These phenomena are of course very 
rare, and few observers will be lucky enough to see one during 
the course of a lifetime. Even the faint, far-off planet Pluto is 
capable of causing stellar occultations; if such a phenomenon 
could be watched, the time taken for the star to remain behind 
the planet would give some indication of Pluto's apparent dia- 
meter, which is still uncertain. Recently, the occultation 
method has been used to re-measure the diameter of Neptune. 

Occultations are interesting, but eclipses are genuinely 
spectacular, and are bound to excite the interest even of the 
non-scientist. A solar eclipse is merely an occultation of the 
Sun by the Moon, but a lunar eclipse is very different, since 
the Moon is not hidden by any solid body, but passes into the 
cone of shadow cast by the Earth. 

The principle is shown in Fig. 31. The Moon has no light 
of its own, so that when it enters the Earth's shadow it turns 
a dim, sometimes coppery colour. The main cone, shaded in the 



diagram, is known as the umbra,* while to either side of it is 
the penumbra, caused by the fact that the Sun is a disk and not 
a sharp point of light. The diagram is not, of course, to scale, 
but it does serve to show what happens. 

'■ . ■ ■v-.-.r? 

Fig. 31. Theory of a lunar eclipse. S — Sun; E — Earth; 

in — the position of the Moon at mid-totality. The diagram 

is not to scale. 

If the Moon passes right into the umbra, the eclipse is 
total. Every scrap of direct sunlight is cut off, but some of the 
Sun's rays will still reach the Moon, as they are bent or 
"refracted" on to it by the Earth's mantle of atmosphere, as 
is shown by the dashed line in the diagram. The result is that 
instead of vanishing completely, the Moon can usually be 
found without difficulty even with the naked eye. However, all 
eclipses are not equally dark. In 1761 the Moon disappeared 
so completely that it could not be seen at all, whereas in 1848 
the totally eclipsed disk still shone so brightly that many people 
refused to believe that an eclipse was in progress. These 
variations have nothing to do with the Moon itself, but are due 
solely to the changing conditions in our own atmosphere. 
It seems for instance that dust in the upper air in 1950, while 
vast forest fires were raging in Canada, caused the September 
eclipse of that year to be rather darker than usual. Abo very 
dark was the eclipse of June 25, 1964, when, from Sussex, I lost 
the Moon during totality even with my isj-inch reflector, 
though conditions were not ideal. The cause on this occasion 
was volcanic dust which had been sent into the upper 
atmosphere by an earlier eruption in the East Indies. By the 
eclipse of the following December, much of this dust had 
settled, and the eclipse was lighter, though still rather dark by 
normal eclipse standards. 

* As used here, the terms "umbra" and "penumbra" have of course no con- 
nection with the umbra and penumbra of sunspots. 



If the Moon does not enter wholly into the umbra, the 
eclipse is partial, while at other times it is merely penumbral. 
Penumbra] eclipses will not be noticed except by the attentive 
watcher, since the dimming is too slight to be conspicuous. 

Two things are clear from the diagram. First, a lunar eclipse 
must be visible from one complete hemisphere of the Earth, 
provided that clouds do not conceal it, and if it is total any- 
where it must be total everywhere. Secondly, an eclipse can 
happen only at Full Moon. If the Moon passes through the 
centre of the umbra, it may remain totally immersed for over 
an hour, while the partial phases can extend over four hours. 

Lunar eclipses are so obvious that they must have been 
known from very early times. Were the Moon's orbit not tilted 
across the ecliptic, a total eclipse would happen at every Full 
Moon, but the inclination of the Moon's path is enough to 
prevent this from happening. Imagine two hoops hinged along 
a diameter, and crossing each other (Fig. 32). The points at 
which the two hoops cross are called the "nodes", and unless 
Full Moon occurs very near a node the Moon will miss the 
shadow altogether, so that no eclipse will occur. 

Fig. 32. Two hoops, demonstrating the tilt of the 
Moon's orbit. 

It so happens that the Sun, Moon and node return to the 
same relative positions after a period of 18 years io£ days, and 
so any particular eclipse will be followed by another eclipse 
18 years 10J days later. This is the so-called Saros Period, and 
was used by the Greek astronomers to make eclipse predictions. 
The Saros is not exact, but the method is accurate enough to be 
workable. A list of future eclipses is given in Appendix IX. 

It is interesting to note the different colours seen on the 
eclipsed Moon, and to see whether the eclipse is bright or dark, 
but the most important work to be done is in connection with 



the Moon itself. Since there is virtually no atmosphere to 
protect the surface, and since the layer of ash is bad at retaining 
heat, the temperature drops suddenly on the lunar surface as 
the eclipse begins. The fall may amount to 100 degrees in the 
course of an hour. 

Some lunar craters cool down less rapidly than their sur- 
roundings during the course of an eclipse. Ray-craters such as 
Tycho are of this type, and have been given the rather mislead- 
ing name of "hot spots". Temperature measurements are still 
of considerable scientific importance, but I do not propose to 
discuss them here, because the equipment needed is beyond the 
range of the average amateur. 


Fig. 33. Theory of a solar eclipse. S — -Sun; M — Moon; 
E — Earth. The diagram is not to scale. 

There have been suggestions that the abrupt cooling during 
an eclipse produces observable effects on certain formations. 
Linne, the feature in the Mare Serenitatis which was once 
suspected of change in form, consists of a craterlet surrounded 
by a white nimbus; various authorities have claimed that the 
white area becomes more prominent during and after the period 
of coldness caused by the eclipse. In spite of the Apollo landings, 
confirmation of this sort of effect would be most important. I 
must admit that my own observations have been negative, and I 
am frankly sceptical, but during the next few eclipses it will be 
worth watching Linne and other features which show white 
surrounding patches. Systematic photography is probably the 
only reliable method of investigation. 

Turning now to eclipses of the Sun, we find that the principles 
involved are very different. We are back to the "occultation" 
idea, since a solar eclipse is caused simply by the Moon passing 
between the Sun and the Earth. 

The Moon is far smaller than the Sun, but it is also so much 
nearer that in our skies it looks almost exactly the same size. 
When the three bodies move into a straight line, with the Moon 



in the middle, the shadow cast by the Moon just touches the 
Earth's surface, and for a few minutes the bright solar disk is 
blotted out by the dark, and therefore invisible, body of the 
Moon (Fig. 33). The width of the completely shadowed area 
of the Earth is 167 miles at best, and so a total solar eclipse will 
not be seen over a complete hemisphere; for instance, the 
eclipse of June 30, 1954 was total in parts of Norway and 
Sweden, but not in England, where it was partial. This means 
that although total eclipses are not particularly rare, they are 
very infrequent at any particular spot on the Earth's surface. 
The last to be visible in any part of England was that of 1927, 
while the next will not occur until 1999. 

To either side of the track of totality, the eclipse will be 
partial, while some eclipses are not total anywhere on the 
Earth. There is also a third kind of eclipse, the annular (Latin 
annulus, a ring). As we know, the Moon moves in an elliptical 
path, so that its distance from the Earth varies. When at its 
most remote, it appears smaller than the Sun in the sky, and 
so cannot cover the whole of the solar disk. When the three 
bodies line up under these conditions, a bright ring of the Sun 
is left showing round the dark mass of the Moon. 

Obviously, a solar eclipse can happen only at New Moon, 
and then only if New Moon occurs near a node. The Saros 
period is valid, as for lunar eclipses, but the rough and ready 
method of forecasdng is less accurate. For instance, the "return" 
of the 1927 eclipse took place in 1945, but in this year the band 
of totality lay further to the north, and missed England 
altogether, so that only a partial eclipse was seen in our 

Partial and annular eclipses are spectacular, but do not give 
much scope for useful work. Remember, too, that even when 
most of the Sun is hidden it is still unsafe to use direct vision 
either with binoculars or with a telescope. The slightest sliver 
of sunlight remaining is enough to damage the eye in a matter 
of seconds, and this was stressed during the large partial eclipses 
visible in Britain in 1954 and 1961, when there were many 
cases of people being injured in this way. 

A total eclipse is among the grandest of Nature's displays. 
As the Moon sweeps on, the light fades, until at the instant the 
last of the disk is blotted out the atmosphere of the Sun leaps 



into view . There are the magnificent red prominences ; there is the 
glorious chromosphere, and there too is the "pearly crown" or 
corona, a superb glow surrounding the eclipsed Sun, sometimes 
fairly regular in outline and sometimes sending out streamers 
across the heavens. It is a pity that the spectacle is so brief. No 
total eclipse can last for more than about 8 minutes, and most 
are much shorter, so that astronomers are ready to travel to 
remote parts of the world in order to make the most of their 
limited opportunities. This enthusiasm is not merely for the 
beauty of the sight; there are many investigations that cannot 
be made except during the period of totality and the few seconds 
before and after. In fact, serious workers are so busy that they 
have no time to stop and admire what is going on. 

The prominences are visible to the naked eye only during 
totality, but with special instruments they can be seen at any 
time. They are made up of incandescent gas, and are of 
tremendous size; the length of an average prominence has 
been given as 125,000 miles. Many are associated with sun- 
spots, and prominences too are affected by the 1 i-year solar 

"Quiescent" prominences are relatively calm, as their name 
suggests, and they may last for several months before either 
breaking up gradually or being violently disrupted. Active 
prominences may be likened to tall tree-like structures, from 
the tops of which glowing streamers flow out horizontally and 
then curve downwards towards the bright surface of the Sun. 
Some of these active prominences are truly eruptive, and it has 
been known for the blown-off material to move at over 400 
miles per second. 

Some of the prominences seen during total eclipses have 
been curiously shaped. One, seen during an eclipse early in the 
present century, bore a marked resemblance to an anteater! 
But since prominence study is not now limited to the period of 
totality, a great deal of information has been gained as to their 
behaviour. French and American astronomers have even taken 
moving pictures of them, and these films are dramatic in every 
sense of the word. 

The pearly corona forms the Sun's outer atmosphere. It is 
much more extended than the chromosphere, and even the 
best instruments of to-day can do no more than show the most 



brilliant parts of it except during an eclipse, so that we still 
have to rely upon the natural screen provided by the Moon. 
The corona is made up of very tenuous gas, and stretches out- 
wards from the Sun for many millions of miles, although 
owing to its low density and indefinite boundary it is not 
possible to give an exact figure for its "depth". 

It is unfortunate that Britain has to wait until 1999 for its 
next total eclipse. Moreover, the coming decade is very eclipse- 
poor so far as Europe is concerned. Other parts of the world 
are more favoured, and no doubt many expeditions will be set 
up. Partial eclipses are, of course, much more common, but it 
cannot really be said that they are of more than passing interest, 
and even an annular eclipse is a very poor substitute for totality. 

It may be of interest to say something about one of the fairly 
recent European eclipses, that of June 30, 1954. It was just total 
off the coast of North Scotland, so that a large partial eclipse 
was seen in England, and caused general interest even among 
people not usually astronomically-minded. The main track 
crossed Scandinavia, where many astronomers gathered. 
The combined Royal Astronomical Society and British 
Astronomical Association party, of which I was a member, 
made its headquarters at the little Swedish town of Lysekil, 
along the coast from Goteborg, since weather conditions in 
West Sweden were expected to be rather better than in 
Norway (as did indeed prove to be the case). Our arrival in 
Lysekil coincided with the Midsummer Festival. It also 
coincided with a burst of torrential rain. 

On June 30, most observers collected their equipment and 
drove to Stromstad, in the exact centre of the track, almost on 
the Norwegian frontier. The site selected was a hill overlooking 
Stromstad itself, and by noon it was littered with equipment of 
all kinds: telescopes, spectroscopes, thermometers, cameras, 
and even a large roll of white paper that I had spread out in the 
hope of recording shadow bands. These shadow bands are 
curious wavy lines which appear just before totality. They are 
due to atmospheric effects, but have seldom been properly 
photographed ; the opportunity seemed too good to be missed.* 

* Unfortunately, conditions at Stromstad were not suitable for the appearance of 
ihadow bands, and none were seen. One eminent astronomer went to the trouble 
of photographing my apparatus, remarking dryly that although he might live to 
see another total eclipse, he would never again see so peculiar an arrangement! 

9 6 


The early stages of the eclipse were well seen. Five minutes 
before totality, everything became strangely still, and over the 
hills we could see the approaching area of gloom. Then, 
suddenly, totality was upon us. The corona flashed into view 
round the dark body of the Moon, a glorious aureole of light 
that made one realize the inadequacy of a mere photograph. 
The sky was fairly clear; and although a thin layer of upper 
cloud persisted, only those with the experience of former 
eclipses could appreciate that we were not seeing the pheno- 
menon in its full splendour. 

It was not really dark. Considerable light remained, and of 
the stars and planets only Venus shone forth. Yet the eclipsed 
Sun was a superb sight indeed, with brilliant inner corona and 
conspicuous prominences. The two and a half minutes of 
totality seemed to race by. Then a magnificent red-gold flash 
heralded the reappearance of the chromosphere; there was the 
momentary effect of a "diamond ring", and then totality was 
over, with the corona and prominences lost in the glare and the 
world waking once more to its everyday life. In a few minutes, 
it was almost as though the eclipse had never been. 

The last total eclipse visible in Europe was that of February 
'5s 1961. The track of totality extended across South France, 
North Italy, Jugoslavia and the southern U.S.S.R., in the 
course of which it covered three major observatories — St. 
Michel in France, Arcetri in Italy, and the Crimean Astro- 
physical Observatory. Much valuable information was ob- 
tained. Again I have personal recollections, since we decided 
to show the eclipse on television, and I was dispatched to the 
top of Mount Jastrebac in Jugoslavia to broadcast the com- 
mentary from there. Amazingly, the programme was success- 
ful, and millions of people all over Europe were able to see 
totality on their television screens. I also remember the 
difficulties I had in communicating with the Jugoslav camera 
director. Eventually I talked French to a Belgian astronomer. 
who relayed it in German to the Jugoslav. The method was 
slightly cumbersome, but fortunately it worked. Clouds hid the 
early part of totality, but by good fortune they cleared in time 
for us to see the end stages and the magnificent "diamond ring". 

The eclipse of September 22, 1968, was inconvenient inas- 
much as the track of totality was confined to a narrow region of 

o 97 


Siberia. After experiencing some visa trouble, I managed to 
travel to Yurgamysh, on the central line, and was rewarded 
with a perfect view. Again the sky was never really dark, and 
totality was short; it was scheduled to last for 43 seconds, but in 
fact the Sun reappeared "ahead of time" between two higldand 
areas of the Moon's limb, and the actual length of totality was a 
mere 37 seconds. As expected, the corona was glorious, and 
there were several magnificent prominences. Despite the usual 
conditions of international tension, astronomers of almost all 
major countries were working away at the eclipse site— in the 
greatest possible harmony. 

A more accessible eclipse was that of March 7, 1970. The 
track of totality crossed Mexico and Florida, and an intensive 
programme of observation was carried out, though only in 
Mexico was the weather really favourable. This eclipse, too, 
was shown on television — and for the first time the pictures on 
the television screen were in full colour. 

The total eclipse of June 30, 1973, was of special interest, 
because over some parts of the track it lasted for over 7 minutes 
— not far short of a record length. The main expeditions were 
in Mauritania and Kenya, but personally I joined the "astron- 
omers' ship", the MS Monte Umbe, which sailed from Liverpool 
to a position between 20 and 25 miles off the coast of North 
Africa. No ship can be completely steady, and all sorts of 
strange devices were set up in order to counter-act the inevitable 
motion. In fact we had remarkably Ikde trouble on this score, 
and although the sky was not completely clear the conditions 
were tolerable. I had decided to search for faint comets near 
the Sun, but thin cloud prevented anything of the sort, and I 
had to content myself with photographing the corona and 
presenting a television commentary. It was a remarkable and 
highly successful voyage; it is safe to say that none of those who 
took part will ever forget it. 

Since total eclipses are so elusive, the opportunity to watch 
one should never be missed, even if no useful work is to be 
attempted. We must be thankful that we are privileged to see the 
spectacle at all. The fact that the Sun and Moon appear so 
nearly equal in size can be due only to chance ; were the Moon 
a little smaller, or a litde more distant, the solar corona might 
still remain unknown. 


Chapter Eight 


It is impossible to separate one science from another. Even 
astronomy is no longer "on its own", as it used to be. It is 
bound up closely with chemistry and physics, and it is also 
linked with weather study, or meteorology, by the phenomenon 
known as the Aurora Polaris, or Polar Light. 

Aurora have been known from very early times, and are 
so common in high latitudes that a night in North Norway or 
Antarctica would seem drab without them. In England they are 
less frequent, though displays are seen on an average at least 
ten times a year, while in the tropics they are rare. They 
are not unknown; there is a famous story of how the cohorts 01 
the Roman emperor Tiberius once rushed northwards to the 
help of the people of Ostia because of a red glow in the sky 
that they took for a tremendous fire, but which proved to be 
merely an aurora. However, there can be no doubt that 
observers in the far north and south have the best views. 

Aurora occur in the upper atmosphere, at heights ranging 
from over 600 miles down to as low as 60. Sometimes the lights 
take the form of regular patterns, while at others they shift and 
change rapidly, often showing brilliant colours and providing a 
spectacle that is second only to the glory of a total solar eclipse. 
One of the greatest displays of modern times took place on 
January 25, 1938, when all Britain witnessed the spectacle. 
From Cornwall "the whole of the western sky was lit with a 
vivid red glow like a huge neon sign; gradually shafts of white 
light were intermingled with the redness, changing quickly to 
an uncanny grey light and then to a brilliant silver, while green 
patches appeared here and there". From Sussex the dominating 
colour was red, though during the course of my own observa- 
tions I recorded many other hues as well. The aurora was 
brilliant and widespread enough to cause interest and even 
alarm over the whole country, and it was seen from places as 
far south as Vienna. 

Since meteorology is the science of the atmosphere, and 



aurora: are definitely atmospheric phenomena, one might 
at first think that they are outside the scope of the astronomer. 
Yet the cause of aurora is to be found not on Earth, but in the 
Sun. Certain active regions of the Sun's disk send out electrified 
particles, and it is these particles which enter our air and give 
rise to the glow, though the process is not completely under- 
stood — and is certainly associated with the so-called Van Allen 
zones, which are belts of charged particles surrounding the 
Earth. The Van Allen belts were quite unsuspected until 1958, 
when they were detected by instruments carried aboard 
Explorer I, the first successful American artificial satellite. 

Active regions on the Sun are often associated with spots, so 
that aurora are most frequent at or near spot maximum. 
Moreover, a major flare occurring near the centre of the solar 
disk is often followed a day later by a bright aurora. Since the 
parades must therefore cover the 93-milUon-mile gap in about 
24 hours, this delay indicates a speed of about 1,000 miles per 

The fact that aurora: occur mainly in high latitudes is due 
not to the geographical poles, but to the poles of magnetism. 
Since the particles which produce the glow are electrified, they 
must be subject to magnetic attraction, and they are often 
accompanied by "magnetic storms", radio fade-outs, and other 
disturbances of like nature. There have even been accounts of 
hissing sounds heard plainly during the course of a display, 
though these noises are difficult to explain. 

Scientifically, aurora are important not only because of 
their link with the Sun, but because they provide information 
about the upper air. It is therefore useful to observe them 
whenever possible, and to make estimates of their positions 
against the starry background, so that their heights may be 
worked out. The main work here has been done by Norwegian 
scientists, led by Professor Carl Stormer of Oslo; but amateurs 
can play a major role, and in recent years a full-scale survey 
has been organized by the British Astronomical Association's 
Aurora Section, which has members all over the world. 
Observers taking part are asked to fill in forms telling of the 
presence or absence of aurora, coupled with notes of any 
displays that may be seen. Negative reports are not without 
value, and may in fact be of great help. 



So far as England is concerned, observing aurora; is made 
difficult by the innumerable artificial lights. My own experience 
is a case in point. From my old home in Sussex I used to be a 
member of the B.A.A. Auroral Survey, but the building of a 
"new town" in the most inconvenient direction caused a 
perpetual glare in the sky, so that my work was brought to an 
abrupt end. Though occasional aurora become so striking 
that they cannot possibly be missed, most displays take the 
form of inconspicuous glows low down in the north or north- 
west, so that the street lamps of a town are enough to obscure 
them. Scottish workers are better placed, both because the 
lights are more scattered and because aurora are much more 

The lights are so varied that to describe all the forms would 
need many pages. One never knows quite what an aurora is 
going to do next, but a great display often begins as a glow on 
the horizon, rising slowly to become an arc. After a while, 
the bottom of the arc brightens, sending forth streamers, after 
which the arc itself loses its regular shape and develops folds 
like those of a radiant curtain. If the streamers extend beyond 
the zenith, or overhead point of the sky, they converge in a 
patch to form a corona (not, of course, to be confused with the 
corona which surrounds the Sun). Finally the display sends 
waves of light flaming up from the horizon towards the zenith, 
after which the light dies gradually away. The whole pheno- 
menon may extend over hours. 

For observing auroras, by far the best instrument is the 
naked eye, coupled with a red torch and a reliable watch. 
Binoculars are of little help, and telescopes absolutely useless. 
Points to note are the bearing of the centre of the display, 
reckoned in degrees (0 to 360) from north round by cast; the 
type and prominence of the aurora; the various forms seen, 
such as arcs, curtains, draperies and flaming surges; colours, 
and duration. Times should be taken at least to the nearest 
minute. There is obvious scope for the photographer, and 
spectroscopic work is of great interest, but simple naked-eye 
observation is not to be despised. 

Though aurora are so spectacular, they are not the only 
fights seen in the heavens. The sky itself seems to shine with 
a feeble radiance known as the airglow, and sometimes a cone of 

1 01 


light can be seen after dusk or before dawn, extending upwards 
from the hidden Sun and tapering toward the zenith. Since it 
extends along the Zodiac, this cone is known as the Zodiacal 
Light, It can be quite prominent when seen from countries 
where the air is clear and dust-free, but from Britain it is always 
hard to see. The Zodiacal Band, a faint, parallel-sided extension 
of the cone, may extend right across the sky to the far horizon, 
though it is so dim that it is seldom to be observed at all except 
from the tropics. 

Unlike the aurora, the Zodiacal Light originates well 
beyond the top of the air. It is thought to be due to light 
reflected from a layer of thinly-spread matter extending from 
the Sun out beyond the orbit of the Earth, rather like a tre- 
mendous plate. The layer cannot be broad, as is shown by the 
fact that the light is never seen except close to the ecliptic. 
The best times for observation are late evenings in March 
and early mornings in September, because at these times the 
ecliptic is most nearly perpendicular to the horizon, and the 
Light is thus higher in the sky. 

Since the Zodiacal Light is faint, so its intensity is not easy 
to estimate. The best way to measure it is to compare it with a 
definite area of the Milky Way, and the width of the base, in 
degrees, should also be noted. Though the Light is pre- 
dominately white, a pinkish or at least warmish glow has been 
reported in the lower parts, and should be looked for. 

Last and most elusive of these glows is the Gegenschein, 
which is a faint hazy patch of fight always seen exactly opposite 
the Sun in the sky. It appears at its most conspicuous in 
September, when it looks like a round luminous patch about 
forty times the apparent width of the Moon, but it is extremely 
hard to sec, and even a distant lamp is enough to hide it. From 
England I have looked for it frequently, but have seen it only 
once— and then not with certainty. There can be no doubt that 
it, too, is caused by interplanetary matter spread thinly 
around the Solar System. The German name is generally used, 
though some prefer the English term of Counter-glow. 

For all these observations, one thing should be borne in 
mind: Never begin work before you have made your eyes 
thoroughly accustomed to the dark. To come outdoors from a 
brilliantly-lit room and expect to see an auroral glow or the 

1 02 


Zodiacal Light straight away is fruitless, and it is usually 
necessary to walk about for at least a quarter of an hour before 
starting your programme, though the exact period is bound to 
vary with different people. For recording observadons, a torch 
with a red bulb is the ideal, since an ordinary white light will 
dazzle you sufficiently to ruin the sensitivity of your eyes for 
some minutes afterwards. 

Here again, then, the amateur has a part to play. There 
is no need to wait years for a great aurora; studying the fainter 
lights and glows is a fascinating hobby, and it is a pity that city 
dwellers never have a chance to see the ghostly beauty of the 
Zodiacal Light. 



Chapter Nine 

Less than two centuries ago, it was thought quite possible 
that the Moon might be inhabited. Sir William Herschel, the 
greatest astronomer of his day, regarded the existence of 
Moon- Men as "an absolute certainty", and we cannot blame 
him. After all, the Earth is an ordinary planet, so why should it 
be the only world to harbour life ? 

As knowledge grew, and the nature of the Moon became 
more and more clear, the "other men" faded away into the 
realms of fantasy; but Mars and Venus, particularly Mars, were 
obviously more promising. And this is one real reason for the 
ever-present interest in the planets : can they, too, be peopled 
by beings at least as advanced as ourselves? 

Today the answer seems to be in the negative. Rocket 
research indicates that Venus is hopelessly hostile ; Mars, too, 
is unwelcoming, and it may be that the Red Planet, once 
believed to be the abode of intelligent life, is as sterile as the 
Moon. Yet this does not make the planets any the less intriguing, 
and from the amateur's point of view no galaxy or variable 
star can be more fascinating than a Martian landscape. 

Even a modest 3-inch refractor will show markings on some 
of the planets, but it is difficult to set a limit for the smallest 
aperture which can be used for serious work. Mars, for instance, 
needs a larger telescope than Jupiter. Each planet has its own 
characteristics, and it is best to consider them one by one. 
^ The four members of the inner group— Mercury, Venus, the 
Earth and Mars— are solid, rocky bodies. They are comparable 
in size, and all have atmospheres of a kind (though that of 
Mercury is extremely tenuous). These are the only common 
factors. Otherwise, they are as different as they can be. 

Mercury, whirling round the Sun at an average distance of 
only 36 million miles, is never easy to observe. It always lies 
somewhere near the Sun's line of sight, and we can well 
understand why it was named after the elusive, fleet-footed 


Messenger of the Gods. Moreover it is not much larger than the 
Moon, and is more than 200 times as distant, so that ordinary 
telescopes will show little except a pinkish disk with its char- 
acteristic phase. 


Fig. 34. Comparative sizes of the Earth, Mercury and 
the Moon, 

The rotation period of Mercury has provided a great deal of 
discussion lately. It used to be thought that the "day" must be 
equal to the "year" — 88 Earth-days in each case. If so, then 
Mercury would always keep the same face toward the Sun, 
just as the Moon does with respect to the Earth. Over part of 
the surface there would be perpetual daylight, with a surface 
temperature exceeding 700 degrees Fahrenheit; over another 
part there would be everlasting night, so that the surface would 
be colder even than remote Pluto. Between these two extremes 
there would be a "Twilight Zone" over which the Sun would 
rise and set. Mercury's orbit is not circular, and so its velocity 
varies between 36^ miles per second at perihelion and only 24 
miles per second at aphelion. This would result in effects 
analogous to the Moon's librations, so producing the Twilight 

Then, however, American scientists used radar methods to 
show that the true rotation period is only 58 \ Earth-days, or 
two-thirds of a Mercurian year. This altered our whole ideas 
about the planet. There is no area of permanent day, no region 
of everlasting night, and no Twilight Zone. 

Our first real knowledge of the surface features was due to the 
U.S. probe Mariner 10. It was launched in November 1973; 



in the following February it flew past Venus, using the gravita- 
tional pull of that world to direct it in towards a rendezvous 
with Mercury. The first active pass of Mercury was made in 
March 1974, and there were two more before the probe finally 
"went silent". Many hundreds of close-range photographs were 
obtained, and it became clear that superficially, at least, 
Mercury is very like the Moon. There are craters, mountains 
and valleys, and even one huge, mountain-ringed structure — 
now known as the Caloris Basin — which looks decidedly 

Less than half of the total surface was surveyed by Mariner 
10, but there is no reason to suppose that the remaining areas 
are fundamentally different. Other interesting facts also 
emerged. Mercury has a definite magnetic field; it is much 
weaker than the Earth's, but it exists, and presumably indicates 
the presence of a large iron-rich core. There is a trace of atmos- 
phere, but the density is so low that it corresponds to what we 
would normally call a vacuum, and it will be of no use what- 
soever to possible astronauts of the future. It is painfully clear 
that so far as Mercury is concerned, any life of the kind we 
know is quite out of the question. 

I have glimpsed a few patches on Mercury, with a 6-inch, 
but little can be seen with amateur-owned telescopes. 
This does not mean that there is no point in looking for 
Mercury. It is always satisfying to see the strange little world 
glittering shyly in the late evening or early morning, and on 
an average it can be seen with the naked eye at least a dozen 
times each year. 

When Mercury is glimpsed without a telescope, it is bound 
to be near the horizon, so that it will be shining through a 
deep layer of the Earth's atmosphere, and the image will be 
unsteady. The best method is to find the planet as early as 
possible, while it is still fairly high up; for sweeping, it is 
advisable to use either binoculars or else a low magnification 
on a small telescope (I have found that a power of 25 on a 
3-inch refractor does very well). A drawing can then be made 
while the sky is still bright. 

Telescopes fitted with equatorial mountings and clock 
drives allow a faint object to be found without any tiresome 
sweeping. This saves a great deal of time, though Mercury is 



never easy to locate except with a large instrument. Yearly star 
almanacs tell where and when it is to be seen, and more detailed 
tables are given in The Handbook of the British Astronomical 

It is also possible to sweep for Mercury in broad daylight, 
but it is never wise to range about with a telescope until 
the Sun has set. Moreover, Mercury and the Sun will not 
be far apart, and there is always the chance that the Sun will 
enter the field of view during sweeping, with disastrous results, 

For examining the phase and for drawing any visible 
surface markings, the magnification used should be as high as 
possible, but the slightest unsteadiness or blurring will be fatal, 
so that one has to strike a happy mean. All things considered, 
Mercury is more difficult to study than any other planet, and it 
is hopeless to expect to see anything spectacular. People who 
live in or near cities will be lucky to find it at all. 

Occasionally, Mercury passes in transit across the face of the 
Sun. When this happens, it can be seen as a well-defined blank 
disk, quite unlike a sunspot. Transits are of no real importance, 
but they are interesting, and projection with a 3-inch refractor 
is quite adequate. The next transit will be that of November 
13, 1986. 

Mercury is so small and remote that even if it did not remain 
obstinately close to the Sun, we could hardly hope to find out 
much about it by observation from Earth. Not so with Venus, 
which is practically the same size as the Eardi, and is the 
nearest body in the sky apart from the Moon. The problems 
here are quite different, but they are equally puzzling. 

Venus is a splendid 
object to the naked eye, 
and can even cast a 
shadow at times, but 
telescopically it is a 
grave disappointment. 
When at its most bril- 
liant, it shows as a cres- 
cent, since by the time 
of "dichotomy" (half 
phase)^ it has already 
drawn away from us, so that its apparent diameter is much 


Fig. 35. Apparent size of Venus at 
various phases. 


less (Fig. 35). Altogether, Venus is a most infuriating object. 

Moreover, the disk appears virtually blank, even with 
powerful telescopes. Vague, dusky shadings may be seen often 
enough, but they are not permanent, and are so diffuse that 
they arc hard to define. In fact, wc are not looking at the true 
surface of Venus at all ; wc are seeing only the upper layers of 
an obscuring atmosphere. 

Up to the end of 1962 our information about Venus as a 
world was remarkably slight. Large quantities of carbon 
dioxide were detected in the upper atmosphere of the planet, 
and there were reports of water vapour as well as a certain 
amount of free oxygen, but even a problem so fundamental as 
the length of the axial rotation period remained unsolved. 
Various estimates were given, ranging from 22 J hours up to as 
much as 224! days; in the latter case the rotation would, 
of course, be "captured" in the same way as the Moon's 
with respect to the Earth, so that Venus would keep the 
same hemisphere turned toward the Sun. Opinions as to the 
nature of the surface fluctuated wildly between a swampy, 
tropical hothouse, a planet completely covered with water, 
and an arid dust-desert without even a scrap of moisture any- 

The only way to decide between these rival dieories was to 
obtain information from probe vehicles. The first successful 
attempt was made in 1962, with America's Mariner 2, which 
by-passed the planet at 21,000 miles and proved that the 
surface really is intolerably hot. Further probes followed. 
Mariner 5 obtained detailed temperature measurements in 
1967, and in 1974 Mariner 10 sent back excellent photographs 
of the cloud-tops as it flew past Venus on its way to Mercury. 
However, it must be admitted that the most important results 
have been obtained by the Russians, who have parachuted 
various probes down through the planet's dense atmosphere. 
In October 1976 two vehicles {Veneras 9 and 10) made soft 
landings, and each probe sent back one picture before being 
put out of action by the hostile environment. The scene was 
gloomy by any standards, with rocks lying everywhere. 
Meanwhile, Earth-based radar measurements by United 
States scientists had established that the surface contains large, 
rather shallow craters. 



The modern view of Venus is not particularly attractive. 
The atmosphere is made up chiefly of carbon dioxide; the 
surface temperature is over 900 degrees Fahrenheit; the 
atmospheric pressure is of the order of 90 to 100 times that of the 
Earth's air at sea-level, and the attractive-looking clouds of 
Venus contain quantities of sulphuric acid. The rotation period 
is 243 Earth-days, which is longer than a "Venus year", and 
the direction of rotation is from cast to west, not west to east. 
Venus has even been described as an upside-down planet. 
Moreover, there is no appreciable magnetic field. 

Though it is so like the Earth in size and mass, Venus is a 
very different sort of place, and it has been nicknamed a 
"hell-planet". Obviously, the chances of sending astronauts 
there are not very high ! Presumably the planet has evolved in 
this unprepossessing way because of the fact that it is consider- 
ably closer to the Sun than we are, though the reason for the 
retrograde rotation is still not known. 

There is no point in observing Venus when it is shining 
brilliantly down from a dark sky; the disk will be dazzling, and 
the image is likely to be violently unsteady. I have found that 
the best seeing is obtained when the planet can just be detected 
with the naked eye, shortly after sunset or shortly before sunrise, 
but observations made in broad daylight are almost as good. 
Venus is so bright that it can usually be found without much 
difficulty even when the Sun is above the horizon. In general it 
will not stand a high magnification, but I have often used 250 
on a 6-inch reflector. 

One line of research is to try to define the positions of the 
dusky shadings, and to follow them as they are carried round 
by the planet's rotation. This was attempted by many observers 
in the time before space-probes could be built, and many 
estimates of the rotation period were published— ranging from 
225 Earth-days down to less than 24 hours. In fact, it has now 
been confirmed that the rotation period of the upper clouds is 
4 days (retrograde) even though the period of rotation of the 
planet itself is so long. This is anotiier puzzle which has yet to 
be satisfactorily explained. 

Bright areas are often seen near the poles, and were indeed 
recorded by Mariner 1 o ; they represent clouds above the polar 
regions, so that they are very different from the white caps of 



Mars. But there is another line of research which is interesting 
to follow up. This involves the exact moment of "dichotomy", 
or half-phase. 

Since the orbit of Venus is known so accurately, it should be 
easy to predict the time of dichotomy, but these predictions 
are usually wrong by several days. When Venus is an evening 
object, observed dichotomy is always early; with morning 
elongations, dichotomy is late. The first astronomer to notice 
this curious disagreement was Schroter, and in writing a paper 
about it years ago I called it "Sch rater's Effect", a term which 
now seems to have been generally accepted. 

There is no chance of Venus being out of position, and the 
effect must be due to the planet's atmosphere. Timing the 
actual date of dichotomy is therefore valuable. The terminator 
will appear sensibly straight for several nights in succession, so 
that a series of observations is necessary. What generally 
happens, of course, is that clouds intervene at a critical stage, 
and cause one to miss a vital evening's or morning's observa- 
tion. Filters can be a help, and it is worth using several in turn 
to check against observations made in ordinary light. 
(Mercury, incidentally, does not seem to show a Schroter 
effect, which is understandable in view of its lack of atmosphere. 
More measurements arc needed, but telescopes of considerable 
power are required, and for this sort of work the refractor has 
the advantage over a reflector.) 

The terminator of Venus shows occasional slight indentations 
and projections. Schroter believed them to be due to differences 
in level, and thought that he had charted a mountain 87 miles 
high (!), but we may now be sure that cloud effects are 

Last, but by no means least, there is the Ashen Light. 
When Venus is a crescent, the night area can often be seen 
shining faintly, so that the whole disk can be traced. The same 
appearance can be seen with the crescent Moon, but the cause 
is different. With the Moon, the glow is due to reflected 
earthlight, but the Earth is certainly unable to illuminate 
Venus, and Venus itself has no moon. Weird theories have been 
advanced to explain the Ashen Light — in 1840, Gruithuisen 
suggested that it might be due to general festival illumina- 
tions lit by the inhabitants of Venus to celebrate the crowning 




of a new ruler* — but some authorities dismiss it as a pure 

contrast effect. 

One interesting theory is that it is caused by brilliant aurora; 
in the upper atmosphere of Venus. Since Venus is closer to the 
Sun than we are, there is no reason to doubt that aurora 
exist, and the explanation is not unreasonable. If we could 
show that the Light is at its brightest during periods of solar 
activity, when terrestrial aurora: are frequent, we might be 
able to clear up the problem. I have made an attempt to 
analyse the available observations of the Light, but unfortu- 
nately the observations themselves are too scattered to be of 
much use. It must however be added that the "aurora" theory 
has been weakened by the revelations that Venus has no 
appreciable magnetic field. 

All the markings on Venus are so indefinite that they are 
hard to record, and there is the added complication that the 
great brilliancy of the disk tends to produce regular, streaky 
patterns that do not actually exist at all. The nebulous aspect 
should be drawn as faithfully as possible, and if the depth or 
sharpness of a shading is exaggerated — as is sometimes necessary 
— the observer must always be careful to write an explanatory 
note beside his sketch. A scale of 2 inches to the planet's 
diameter is convenient. 

We know a great deal more about Venus than we used to in 
the pre-Space Age, but many problems remain, and will not be 
easy to solve. Even transits are irritatingly rare, and the next 
will not occur until a.d. 2004. So let us turn to Mars, which is 
frankly a more rewarding object inasmuch as it does show 
permanent surface markings. 

Mars can approach us to a distance of 35 million miles. 
It is therefore always at least 150 times as remote as the Moon, 
and it is much smaller than the Earth, with a diameter of 
only 4,200 miles. Fortunately, it is better placed than either 
Mercury or Venus. Since it lies beyond the Earth's orbit, it 
can never appear as a half or a crescent, while at its most 
gibbous it looks the shape of the Moon two or three days from 

The main trouble about observing Mars is that it comes to 

* Sometimes the Light may be seen several times per week, so on Gruithuisen'* 
theory the Government of Venus would seem to be somewhat unstable! 



opposition only at intervals of nearly two years, as explained 
in Chapter 4. We can see fine details only for a few weeks to 
either side of opposition,* so that the opportunities for useful 
work are brief; the observer has to make the most of the limited 
time at his disposal. Nor are all oppositions equally favourable, 
because Mars has an orbit that is more elliptical than ours. 
When opposition occurs with Mars near perihelion, the distance 
is relatively small; at an aphelic opposition, such as that of 
1963, the distance may never be less than 60 million miles. In 
Fig, 36, the orbits of the two planets are shown, with the 
opposition positions for 197 1 to 1986. 

The 1956 opposition was the best of recent years, though 
from Britain Mars was too low in the sky to be well observed. 
The opposition of 1958 was almost as close, but that of 1961 
was less favourable, while those of 1963 and 1965 were even 
worse. Then came some good oppositions (1971, 1973 and 
1975), but those of 1980 and 1982 will not be so favourable. 

When at its brightest, Mars is actually more brilliant than 
any other planet apart from Venus. It can even surpass Jupiter. 
However, this is the case only at very favourable oppositions, 
and when at its furthest from us Mars sinks to below magni- 
tude i|. 

Mars has a "year" of 687 Earth days, and the tilt of the 
axis is much the same as ours, so that the seasonal cycle is 
similar. Since it has an average distance of about 141 million 
miles from the Sun, compared with the 93 million of the 
Earth, we must expect it to be cool ; but it is certainly not a 
frozen world. The maximum summer temperature on the 
equator may attain 60 degrees Fahrenheit, and though the 
nights are bitterly cold they are not unendurable. The axial 
rotation period is 24 hours 37 minutes, and the surface gravity 
only 4/10 of ours. If an Earthman stood upon Mars, he would 
be able to jump more than ten feet above the ground. 

The beginner is apt to be disappointed with his first tele- 
scopic view of Mars. Whereas he may expect to see avast globe 
streaked with canals and blotched with obvious vegetation 
areas, he generally sees nothing except a minute reddish 

* It is often thought that Mars can be well seen onJv on the actual date of oppo- 
sition, whereas in fact there is no obvious difference in observing conditions for an 
appreciable time to either side of the opposition dale. 


Fig. 36. Oppositions of Mars 1971-1986. 
It will be seen that Mars is at its closest 
when opposition takes place near Martian 
perihelion, as in 1971- 


disk crowned in the 
north or south with 
a whitish cap. It is 
only when he has 
become thoroughly 
used to planetary 
work that he can 
make out definite 
detail. The markings 
on Mars are much 
less spectacular than 
the belts of Jupiter, 
the rings of Saturn 
or even the phases 
of Venus. Even the 
polar caps become 
invisible with a small 
telescope when they 
are not at their most 
extensive. We must 
also bear in mind the fact that Mars sometimes develops 
atmospheric dust-storms which conceal the surface features 
completely. I well remember that during the perihelic opposi- 
tion of 1 971 there were weeks when I could record nothing 
on the surface, even though I was using my 15-inch reflector 
under good seeing conditions. 

The first good map of Mars was drawn in 1877 by the Italian 
astronomer G. V. Schiaparelli, using an 8f in. refractor. 
Schiaparelli charted the bright and dark areas very accurately, 
and allotted names which are still in use. He also described a 
network of straight, artificial-looking lines, which he called 
"canali" (channels) but which are always known as the Mar- 
tian canals. Inevitably, the suggestion was made that these 
canals might be artificial. Percival Lowell, who built a major 
observatory at Flagstaff (Arizona) mainly to study Mars, was 
convinced that die Red Planet supported an advanced tech- 
nical civilization, and that the canals represented an irrigation 
system to carry water from the polar snows through to the arid 
deserts of the equator. 

Lowell's views met with considerable opposition even in his 

e 113 


lifetime, though he remained unshaken up to the time of his 
death in 191 6. The idea of intelligent Martians was regarded as 
distinctly dubious. On the other hand, the idea that the dark 
areas were due to vegetation met with strong support, and up to 
1965 very few astronomers doubted it. 

One piece of evidence, often quoted, was that of the so-called 
"wave of darkening" bound up with the seasonal cycle of the 
polar caps. There is no doubt at all that the caps change 
according to the time of year on Mars; during Martian winter 
a cap is large, but it shrinks rapidly with the oncoming of 
warmer weather, and in midsummer it becomes very small. 
(On some occasions the southern cap has been known to 
vanish completely.) It was claimed that when a cap shrank, 
the dark areas near its border became harder and sharper, as 
though the lowly vegetation were being revived by the moist 
winds. Everything seemed to fit in, and most astronomers were 
confident that the overall picture of conditions on the Martian 
surface was not far from the truth. 

I was always something of a sceptic about this "wave of 
darkening", but I was in no real doubt that Mars was well able 
to support life of a kind, and it seemed probable that the famous 
grey patches were depressions — presumably the beds of dried- 
up seas. The atmospheric pressure was thought to be around 85 
millibars, equivalent to the density of the Earth's air at a height 
of between 50,000 and 60,000 feet above sea-level, and most 
authorities believed that the main atmospheric constituent 
must be nitrogen. 

Then, in 1965, came the flight of Mariner 4— and all these 
optimistic impressions were rudely shattered. Television 
pictures sent back from within a few thousand miles of the 
Martian surface showed that instead of being smooth, the 
planet was extremely rugged; there were large craters, together 
with mountains and valleys. Better pictures were obtained from 
Mariners 6 and 7, of 1969, but the bulk of our present know- 
ledge has been drawn from Mariner 9, which was sent up in 
1 97 1. Instead of by-passing Mars, it was put into a closed path 
round the planet, and sent back thousands of close-range 

The results were dramatic. Mars is a world of giant volcan- 
oes, huge craters and spectacular valleys which look very much 

ti 4 


as though they have been water-cut. Some of the volcanoes, 
such as Olympus Mons, arc of "Hawaiian" type, but are 
much loftier and more massive than any volcanoes on Earth ; 
indeed, they dwarf mountains such as those of our Himalayas, 
Just as interesting are the valleys, which seem to make up parts 
of drainage systems away from the volcanoes. Such is the 
Tithonius Lacus— (now re-named Vallcs Marineris), which 
proves to be a tremendous formation with what seem to be 
tributaries extending from it. Of special interest is Hellas, the 
circular feature south of the V-shaped Syrtis Major. Instead of 
being a high plateau, it turns out to be the deepest depression 

on Mars. 

There can be no doubt at all that we are looking at volcanoes, 
and we cannot be at all sure that volcanic activity is absent at 
the present time. When Mariner 9 arrived near Mars, in 
November 1971, the planet was veiled by a global dust-storm, 
and it took weeks before the dust settled and photography of 
surface could begin. The general explanation of storms such 
as this is that the material is whipped up from the "deserts" 
by winds, but it has also been suggested that dust sent out from 
the volcanoes could be responsible. Moreover, the valleys show 
remarkably little erosion, and can hardly be more than a few 
tens of millions of years old at most. If this is the case, then 
Mars must then have had much more water, and therefore 
much more atmosphere, than it has now. 

Note, also, that the dark regions are not depressions; some, 
such as the Syrtis Major, are raised. They seem to be distin- 
guished only by their colour, not by any marked difference in 
terrain, which is yet another surprise. 

Yet perhaps the most important results from the Mariner 
probes relate to the planet's atmosphere. We now know that 
far from being reasonably dense, it is very thin ; the pressure no- 
where exceeds 10 millibars, and the main constituent is carbon 
dioxide. All in all, Mars is much less welcoming than we had 
expected, though from the geological point of view it is fascin- 

Then, in 1976, came the epic soft landings of Vikings 1 and 
2, in Chrysc and Utopia respectively. Magnificent pictures were 
obtained of the rock-strewn surface, and the only real dis- 
appointment was the failure to detect any organic material — 



so that Mars may be sterile. The orbiting sections of the Vikings 
proved that the north polar cap is made up chiefly of ordinary 
ice, with a seasonal coating of solid carbon dioxide, while the 
south cap seems to be a mixture of water ice and CO a ice. 
Incidentally, we must now finally forget Lowell's canaf net- 
work, which does not exist in any form. 

Bad drawings of Mars are regrettably common, even in 
textbooks. Crude draughtsmanship can be forgiven, but an 
observer who uses a 3- or even a 6-inch telescope to record 
dozens of canals is deceiving himself as well as others. It 
is very easy to "see" what one expects to see, and for this 
reason it is best to go to the telescope with a completely open 
mind. Tables given in The Handbook of the British Astronomical 
Association can be used to work out the longitude of the central 
meridian for any particular time, but such calculations should 
be made after the observation and not before. 

Since drawings of Mars have to be made with comparatively 
high magnifications, the planet is a difficult object for small 
telescopes. A 3-inch refractor will show the caps and some of 
the main dark areas, such as the Syrtis Major and the Mare 
Acidalium, but for useful work at least a 6-inch is needed, while 
an equatorial mount and a clock drive should be added if 
possible.* A scale of 2 inches to the planet's diameter is 
customary; when the phase is evident, as is always the case 
except near opposition, the disk should be drawn to the correct 

_ Begin, as always, by looking carefully at Mars for some 
time until your eye has become thoroughly prepared. Then 
sketch in the main details, the caps and dark areas, using a 
moderate power. Change to the highest magnification that will 
give a sharp, steady image, and fill in the finer detail. As soon as 
this has been done, note the time, and make a record of it 
below your sketch. This is important; Mars spins on its axis 
in 24 hours 37 minutes, so that the drift of the markings across 
the disk becomes noticeable over even short periods. (Obviously, 
any particular marking will pass over the central meridian of 

• In his excellent book ObstToational Astronomy Jot Amateurs, J. B. Sidgwick states 
that an equatorial is "a necessity" and a drive "virtually so". This is ccrtainiv 
incorrect. W. F, Denning, one of the greatest planetary observer! of the late 
nineteenth century, always used a telescope mounted on a "simple altazimuth, and 
was awarded the Gold Medal of the Royal Astronomical Society for his work. 



Mars about half an hour later each night, since the rotation 
period is half an hour longer than ours.) Finer details can 
then he added without undue haste. Colours, intensities of the 
dark areas, and any clouds should always be looked for, as 
well as features such as a dark border to the polar cap, seen 
when the cap is shrinking and formerly attributed to temporary 
moistening of the ground. 

Very small telescopes are useless for serious work on Mars, 
but oddly enough it has been stated that giant instruments also 
are unsuitable. Sidgwick states* that "if the aperture exceeds 
about 12 inches, the atmosphere will seldom allow the full 
aperture to be used". This is a well-worn argument, but it is 
completely false. It is true that an increased magnification will 
also increase any tremor due to the air, but under normal 
conditions a large telescope will always show more than a small 
one. This has been my own experience with instruments 
ranging from a 3-inch refractor up to a 33-inch, and it is 
significant that E. M. Antoniadi, whose work has formed the 
basis of most modern investigations of Mercury, Venus and 
Mars, used the Meudon 33-inch for his main research without 
the slightest temptation to stop down the aperture. However, 
a reflector of from 8- to 1 2-inches aperture is enough to allow 
the amateur to play his part in the observing programme for 
Mars. Drawings made with smaller apertures are bound to be 
rather suspect. 

In view of all that has been achieved with the various 
probes, it may be asked: What can the amateur observer still 
do? The question is reasonable enough — but there is a firm 
answer to it. Mars, remember, has an atmosphere, and it is 
certainly not a static world. Dust-storms occur, and studies of 
them are of great value ; the same is true of observations of the 
well-defined clouds which can sometimes be seen, since the 
movements of these clouds can help us toward a better under- 
standing of the Martian wind systems. Obviously, we cannot 
see the craters in their true guise, but we can follow the chang- 
ing sizes and shapes of the polar caps. Then, too, there are the 
not infrequent irregular alterations in the forms and inten- 
sities of the dark areas — the cause of which is still a mystery. 

* J. B. Sidgwick, Observational Astronomy for Amateurs, Faber & Faber, London, 
'955- p age "7- 



Owners of larger instruments may care to look for the two 
tiny moons, Phobos and Deimos. Both are veritable dwarfs less 
than a dozen miles in diameter, so that even when Mars is 
near opposition they are difficult to glimpse. I have seen them 
both with a 15-inch reflector, and keener-eyed observers should 
catch sight of them with a 12-inch when conditions are first-class. 

A rather stupid mistake on my part may serve to show 
that it is not wise to reject an observation because it does not 
"fit in" with what is expected. I was once observing Mars with 
my I2|-inch reflector, when I recorded a minute starlike 
point, clearly visible only when Mars itself was hidden by an 
occulting bar, which I took to be Phobos. I then consulted my 
tables, and found that Phobos was not in fact anywhere near 
the position recorded. I therefore dismissed the observation, 
as either a mistake or else an observation of a faint star. It was 
only on the following day that I found that the observation 
itself was perfectly correct ; I had made a slip in my calculations. 

Phobos is a peculiar little body. It whirls round Mars at a 
distance of only 3,800 miles above the surface, about as far as 
from London to Aden, and it completes one revolution in only 
~]\ hours. So far as Phobos is concerned, the "month" is shorter 
than the "day", and to a Martian observer Phobos would seem 
to rise in the west, gallop across the sky — taking only 4^ hours 
to pass from horizon to horizon— and set in the east. Neither it 
nor Deimos would be of much use as a source of moonlight, and 
Deimos would indeed look like a large, dim star. 

Both satellites were photographed from Mariner 9 and the 
Vikings. Each is irregular in shape, and each is pitted with 
craters. Phobos and Deimos are quite unlike our own Moon, and 
probably they are nothing more than ex-asteroids which were 
captured by Mars in the remote past. Iosif Shkiovsky, a famous 
Russian astronomer, once suggested that they were nothing 
more nor less than hollow space-stations, launched by the 
Martians for reasons of their own; but I fear that the latest 
probes have put paid to this attractive, if somewhat remarkable, 

Our knowledge of Mars has grown out of all recognition 
since 1965. Where we had hoped to find a life-bearing world, 
with vegetation tracts and a reasonably useful atmosphere, 
we have in fact found a planet which is hostile even by the 



most tolerant standards — and which remains probably the 
most intriguing world in the entire Solar System. The massive 
volcanoes, the deep rift valleys and the craters give a landscape 
which is totally unlike that of the Earth, and not really similar 
to that of the Moon. We cannot yet dismiss the possibility of 
low-type life, though I have to admit that I regard it is unlikely. 
We cannot yet say when Mars will be reached by pioneers 
from Earth. Technically, a voyage there may be possible by 
2000, and it should have been achieved well before 2050. 
Whether permanent colonies can be set up there is a question 
which ought to be solved within the next few decades. 


Chapter Ten 


As soon as we look at a scale map of the Solar System, 
it is seen that the division of the planets into two main groups is 
very pronounced. Between the orbits of Mars and Jupiter there 
is a wide gulf of over 300 million miles. 

Nearly 200 years ago, Johann Bode suggested that there 
might be a small planet revolving round the Sun at a distance 
of about 260 million miles. There were sound reasons for 
believing that he might be right, and towards the end of the 
century a group of six leading astronomers, headed by Schroter 
and the Baron von Zach, began a systematic search for the 
missing body. Oddly enough, they were forestalled. Before the 
scheme was in working order, Piazzi at Palermo happened upon 
a starlike object that turned out to be a small world circling 
the Sun at almost the correct distance. It was named Ceres, in 
honour of the patron goddess of Sicily. 

Ceres is a dwarf world only 650 miles in diameter, so that it 
must be totally without atmosphere, and is a mere lump of 
rock devoid of any kind of life or activity. But it seemed too 
insignificant to be a major member of the Sun's family, and 
Schroter and his "celestial police" continued with their pro- 
gramme. Between 1801 and 1808 they discovered three more 
minor planets, and when a fifth was added in 1845 it became 
clear that the original four were merely the brightest members 
of a whole shoal. Since 1848 no year has passed without fresh 
discoveries, and over 2,000 of these minor planets or "asteroids" 
are now known, while the total number has been estimated as 
at least 40,000. 

Ceres remains the largest known of the swarm, and of the 
rest only Vesta and Pallas have diameters exceeding 300 miles. 
Some are real midgets less than a mile across, so that there is 
no definite distinction between a very small asteroid and a very 
large meteor. Of all the minor planets, only No. 4, Vesta, can 
be seen with the naked eye when at its brightest. The rest are 
always invisible without a telescope. 



Hunting and photographing asteroids is a pleasant pastime, 
and it is not difficult. I once spent an evening searching for 
known asteroids with a 6-inch refractor, and observed fifteen 
of them in only two hours, though I could not identify them all 
until I re-observed on the following night. 

The procedure is to look up the position of a suitable asteroid, 
using an almanac or the B.A.A. Handbook, and plot it on your 
star chart. Then go to the telescope, and search until you have 
found the desired star-field, using the method described in 

Fig. 37. Apparent shift of the minor planet Pallas over 
a period of 24 hours; Patrick Moore, 3-in. refractor. 

Chapter 15. As the minor planet will look exactly like a star, it 
will not be recognizable at first sight, so the only course is to 
make a map of all the stars in the area. When you look again 
the following night, the stars will be unchanged, but the minor 
planet will have betrayed itself by its obvious shift in position. 
Two drawings of this kind are shown in Fig. 37. 

Though most of the minor planets remain in the main zone 
between Mars and Jupiter, some have unusual paths. The 
"Trojans" are exceptionally remote, and have the same mean 
distance as Jupiter, so that they are very faint, whereas the 
extraordinary asteroid Hidalgo has an eccentric orbit that 
carries it from inside the path of Mars out almost as far as 
Saturn. And in 1977 C. Kowal, at Palornar, discovered a 
400-mile asteroid, Chiron, whose orbit lies between those of 
Saturn and Uranus. 

Even stranger are the occasional minor planets which make 
close approaches to the earth. Eros, the largest of them, has a 
minimum distance of 15 million miles, and has been most 



useful in helping astronomers to measure the length of the 
"astronomical unit", the mean distance between the Earth and 
the Sun, though admittedly the Eros method has now been 
superseded. Other "Earth-grazers" can come even closer. The 
present holder of the record is Hermes, only a mile in diameter, 
which whirled by us in 1937 at a distance of only about 480,000 
miles. This is still twice as far away as the Moon, but when the 
news was released there were some people who became really 
alarmed at the idea of a celestial collision, while one national 
newspaper produced the immortal headline: "World Disaster 
Missed by Six Hours." Actually, the chances of our being hit 
by an asteroid of any size are so small that they can be neglected. 
Oddest of all the minor planets is Icarus. At aphelion it lies 
beyond the orbit of Mars, but at perihelion it swings to within 
19 million miles of the Sun. It is then closer than Mercury, and 
its "day" side must be red-hot. In 1968 it approached the 
Earth to within 4 million miles, but there was no danger of a 
collision, despite some sensational reports in the Press! Its 
diameter is no more than 2 miles. 

Beyond the main asteroid zone we come to mighty Jupiter, 
giant of the Solar System. Though it never approaches us much 
within a distance of 360 million miles, well over a thousand 
times as remote as the Moon, Jupiter still shines so brilliantly 
in our skies that it cannot be mistaken for a star. It is outshone 
only by Venus and, very occasionally, by Mars. 

Jupiter's vast globe could contain 1,300 bodies the size of the 
Earth, but it is not so massive as might be supposed. If we 
could put Jupiter in one pan of a pair of scales, we should 
need only 318 Earths to balance it. This must mean that 
Jupiter is less dense than the Earth, and the density works out 
at only 1 -3 times that of water. 

Jupiter is not a rocky body like the Earth or Mars. When we 
look at it through a telescope, what we see is not a hard surface, 
but a cloudy vista with details which change not only from night 
to night, but from hour to hour. We must not, however, draw 
any comparison with Venus. Jupiter's "atmosphere", to use the 
word in a broad sense, is so deep that it merges with the true 
"body" of the planet. 

It used to be thought that Jupiter consisted of a rocky core, 
overlaid by a 15,000-mile thick layer of ice which was again 



overlaid by the atmosphere. Recent research has cast doubts 
upon this theory, and it is now generally believed that there is a 
relatively small rocky core, overlaid by liquid hydrogen which 
is in turn overlaid by the atmosphere. 

At any rate, we can carry out analysis of the upper gas, 
which proves to be an unprepossessing mixture of ammonia, 
methane and free hydrogen. Both ammonia and methane are 
poisonous, and when it is remembered that the temperature 
on Jupiter can never rise above —200 degrees Fahrenheit we 
can see that any form of life there is out of the question. 

In a small telescope, Jupiter appears as a yellowish disk, 
flattened at the poles and crossed by prominent streaks known 
as "belts". Increased power shows finer details such as wisps. 
brightish areas and spots. Though all these are phenomena of 
the high atmosphere, studies of them can tell us much about 
Jupiter itself, and amateur work in past years has been of the 
greatest value. The records of the Jupiter Section of the British 
Astronomical Association, directed for many years by the Rev. 
T. E. R. Phillips and now by W. E. Fox, are the most complete 

in existence. 

The belts, due probably to droplets of liquid ammonia, 
dominate the picture. Usually there is a prominent belt to 
either side of the equator, while moderate telescopes will 
reveal others. They vary in prominence, as becomes evident 
if observations are continued from year to year. In 1 962-1964 
the general aspect was most unfamiliar, since the two equatorial 
belts ran together to form a dark band, but by 1966 the appear- 
ance was back to normal. 

Spots are generally short-lived, and last only for a brief 
period before disappearing. The chief exception is, of course, 
the famous Great Red Spot, which became very striking in 1878 
and can be traced on drawings made as early as 1631. In its 
prime, the Spot was a brick-coloured elliptical object 22,000 
miles long and 7,000 wide (Fig. 38). It disappears at times, but 
it always returns. The Pioneer probes which by-passed Jupiter 
in 1973 and 1974 respectively, indicate that the Spot is a kind 
of whirling storm— a phenomenon of Jovian meteorology, not 
a "floating island" as was once believed. It is the only feature 
of the disk which has been known to persist for more than 
half a century, its nearest rival in this respect being a 



disturbance in the south tropical zone which lasted from iqoi 
to 1940. 

If Jupiter is watched for a few minutes with a magnification 
of 150 or more, the surface features will be seen to be drifting 
slowly from right to left. This is the result of the planet's axial 
spin, and is more obvious than in the case of Mars, since 
Jupiter has a much shorter "day". In the tropical zone, 
between the two equatorial belts, the period is only 9 hours 
50$ minutes, while in higher latitudes it is 5 minutes longer. 
Jupiter does not rotate as one mass; different zones have 
different rates of rotation, and this is an extra proof that the 
surface we see is not a solid body. 

vCv >x w:-x-w.' 

f Eorfh j 

Fig. 38. Size of the Great Red Spot. 

Moreover, individual features have individual rotation 
periods. Between 1901 and rg^o the Red Spot and the South 
Tropical Disturbance were both to be seen, and the Dis- 
turbance moved the more quickly of the two. Periodically it 
caught up the Spot and "lapped" it, and when the two were 
close together they seemed to interact. (In 1966 what seemed 
to be a new South Tropical Disturbance was detected by 
T. J. C. A. Moseley at Armagh; I saw it shortly afterwards, 
and we had high hopes of it, but to our disappointment it 
faded away after a few weeks.) In 1919-20 and in 1931-34, 
observers of the B.A.A. Jupiter Section even observed "cir- 
culating currents" in the south tropical zone, and many other 
interesting examples could be given. 

Jupiter's quick rotation means that one cannot afford to 
linger when making a disk drawing. The sketch should be 
completed in less than 10 minutes, as otherwise the drift of the 
surface features will introduce errors. As in the case of Mars, the 
main details should be filled in first; the time should then be 
noted, after which the magnification can be increased and the 
finer details added. 



One minor irritation is that one cannot use a pencil compass 
to draw the outline of the disk. The polar compression amounts 
to 6,000 miles (as against 26 miles in the case of the Earth) 
so that it cannot be neglected, and shaping the outlines free- 
hand is a tedious process. I have found that the best solution 
is to obtain a stock of blanks, as shown in Fig. 39. These blanks 
are not expensive to have printed, and any local firm will 
make them at low cost. 

Fig. 39. This diagram can be traced and a line-block 
obtained so that a printer can run off a stock of blanks. 

Rotation periods of special features are best determined by 
the method of transits. There is no analogy with the solar transits 
of Mercury and Venus, and the word is used to denote the 
time when the feature under study passes across the central 
meridian of Jupiter. 

What is done is to estimate the time of transit to the nearest 
minute, which is quite adequate. A measuring device is 
naturally helpful, but visual estimates can be made quite 
accurate enough for most purposes, and Jupiter rotates so 



rapidly that it is often possible lo time 20 or 30 transits per 
hour. There is a standard nomenclature, and this is given in 
Appendix VII, together with an extract from my own note- 
book that may prove helpful. It is hardly necessary to add that a 
reliable watch is essential — and make sure that it is set to the 
correct G.M.T.! 

Once the time of transit has been found, the longitude of 
the feature can be found by means of the tables in the B.A.A. 
Handbook. This is an easy process, and involves nothing more 
frightening than simple addition. 

Transits assumed unexpected importance in 1955, when two 
American researchers, B. F. Burke and K. L. Franklin, found 
that Jupiter emits long-wave radiation of the type known 
scientifically as "radio noise". The discovery was surprising, 
and the radio astronomers naturally wanted to know whether 
the emission came from the whole planet, or merely from small 
active regions of the disk. If the latter, the radio emission should 
be at its most powerful when the feature concerned is on the 
central meridian. It now seems that there is no correlation 
between visual features and radio emissions. Pioneer 10, in 
'9 73 > showed that Jupiter has a complicated, very strong 
magnetic field, and intense zones of radiation — which came 
within an ace of putting Pioneer's instruments out of action! 
This was confirmed by Pioneer 11, which made its pass of 
Jupiter in December 1974. We should learn more from the two 
Voyager probes which are now on their way. 

For routine work on Jupiter, a power of 150 to 250 on a 
6-inch reflector is adequate. Transits can be taken as accurately 
as with a larger instrument, but there will be fewer observed, 
since only the major features of the disk will be visible. 

As befits the senior planet of the Solar System, Jupiter 
has a retinue of 13 or 14 moons or satellites. Four of them are 
bright enough to be seen with any telescope, and there are 
records of their having been seen with no optical aid at all, 
but the others are too dim to be glimpsed with any amateur- 
owned equipment. 

The four main satellites are lo, Europa, Ganymede and 
Callisto. For many years the minor attendants were unnamed, 
but they have now been officially christened. Satellite V 
(Amalthea) is closer in than the large satellites. In order of 



increasing distance, the outer dwarfs are: XIII (Leda), VI 
(Himalia), X (Lysithca), VII (Elara), XII (Ananke), XI 
(Carme), VIII (Pasiphae) and IX (Sinope). A fourteenth 
satellite reported by Kowal has not been confirmed, and 
obviously has not been named, but it probably exists. I have no 
doubt that there are several more midget attendants awaiting 
discovery, but they are bound to be excessively faint, and 
completely beyond the range of most telescopes. 

lo and Europa are about the size of our Moon, while 
Ganymede and Callisto are larger, and actually of greater 
diameter (though lesser mass) than Mercury. Surface details 
can be seen only with great telescopes, but the movements of 
the four "Galileans" are fascinating to watch; any small instru- 
ment is adequate. 

Since all four revolve approximately in the plane of Jupiter's 
equator, they appear to keep in almost a straight line, but it 
often happens that one or more of them is missing. A satellite 
may pass in front of Jupiter, appearing in transit;* it may pass 
behind, and be occulted; it may pass into Jupiter's shadow, 
suffering eclipse. The transits are particularly striking. In Plate 
VIII (c), a typical view, the dark disk of Ganymede is seen 
against the Jovian clouds. Accurate timing of these phenomena 
is valuable. All these transits, eclipses and occultations are 
predicted for each year in the B.A.A. Handbook, and in many 

The remaining eight satellites are among the faintest 
observable objects in the Solar System. Amalthea, which lies 
closer to Jupiter than any other member of the retinue, has been 
recorded with an 18-inch under the best possible conditions, 
but Leda has never been "seen" visually, though it has 
left its image on photographic plates. The diameters range 
from 150 miles (Amalthea) down to only about 5 miles 
(Leda), so that they are inferior to many of the asteroids. 
Their orbits are strange; the outer four are so distant from 
Jupiter that they take over a year and a half to complete one 
revolution, while to make matters even more complicated 
Ananke, Carme, Pasiphae and Sinope go round the wrong way, 
east to west instead of from west to east. These four are so far 

* This is yet another use of the word "transit". A satellite transit has nothing 
to do wish the apparent passage across Jupiter's central meridian, 



out that even Jupiter's mighty pull is barely sufficient to 
control them, and consequently their orbits are not even 
approximately circular. Pasiphae, discovered in 1908, was 
actually "lost" for some time after 1941, and was not found 
again until 1955, Possibly these moonlets are not true satellites 
at all, but merely minor planets that have been captured by 
Jupiter and forced to give up their independent status, 

Far beyond Jupiter, at an average distance of 886 million 
miles from the Sun and a minimum of 741 million from the 
Earth, lies Saturn, second of the giant planets. In itself Saturn is 
less important than Jupiter; it is smaller, with an equatorial 
diameter of 75,100 miles and a mass of 95 times that of the 
Earth, and it is made up in much the same way. It is even colder 
than Jupiter, since the temperature never rises above —240 
degrees Fahrenheit, and it too must be utterly lifeless. 

Saturn shows belts and spots, but surface features are much 
less conspicuous than those of Jupiter, and well-marked spots 
are very rare. The last really spectacular outbreak took place in 
1933, when W. T. Hay (Will Hay), a famous comedy actor 
who was also a skilled amateur astronomer, discovered a 
short-lived white spot near the equator. I detected a fainter 
white spot in 1962, but it never became prominent, and soon 
faded away. Features of this kind can be used for transit 
observations, as in the case of Jupiter, but they are so unusual 
that our knowledge of Saturn's rotation period is far from 
complete. The value for the equatorial zone seems to be 10 
hours 14 minutes. 

Saturn is a quieter world than its giant brother, but the 
various zones seem to show changes in brightness, so that 
intensity observations are of value. These can be made by eye 
estimates, on a scale of o (brilliant white) to 10 (black shadow). 
The work needs a telescope of at least 8 inches aperture, but 
fortunately Saturn is a convenient object inasmuch as it will 
usually stand a comparatively high magnification. 

But the glory of Saturn lies in its ring system. Huygens, the 
leading telescopic worker of the seventeenth century, described 
it as "a flat ring, which is inclined to the ecliptic and which 
nowhere touches the body of the planet", but actually there are 
three rings, two bright and one dusky (Fig, 40). The whole 
system has a diameter of almost 1 70,000 miles. 



Saturn is a massive planet, and it has a strong gravitational 
pull. Were the rings liquid or solid, they would soon be broken 
up and destroyed, so that they must be made up of individual 
particles whirling round Saturn like miniature moons. It is 
possible that they are the shattered remnants of a former satellite 
that wandered too close to its master. 

A 3-inch telescope will show the rings, but in a 6-inch the 
sight is glorious indeed, and Saturn is without doubt the most 
superb object in the heavens. It is unique in its glory, and it is a 
sight never to be forgotten. 

Crepe Ring 

Ring A 


Fig. 40. Diagram of Saturn's ring system. 

Details can be seen in the ring-system. The bright rings, A 
and B, are separated by a dark area known as Cassini's Divi- 
sion, in honour of its discoverer. The Division is a true gap, and 
is due to the disturbing influences of Saturn's satellites. There is 
a second gap in Ring A (Encke's Division) which can be seen 
under good conditions with an 8-inch reflector, and other 
divisions have been reported, though they have not been fully 
confirmed and their existence is doubted by many observers.* 

Though the rings cover so vast an area, they are strangely 
thin, far thinner relatively than a sheet of tissue paper. They 
cannot have a thickness of more than 50 miles, and 10 miles is 
probably nearer the truth, so that when they are placed edge-on 
to the Earth they almost disappear. The drawings in Fig. 41 
show the alterations in appearance from year to year. The rings 

• I have looked for these divisions with telescopes ranging from 10 to 33 inches 
aperture, but have seen only Cassini's and (occasionally) Encke's. Neither have I 
been able to find a fourth "dusky" ring lying outside Ring A, reported on various 
occasions since 1909, or a reported ring between the Crfpe Ring and the globe. 
Frankly, I am sceptical about these extra rings. 

1 129 


were edge-on in 1950 and 1966; they will again be edge-on 
in 1979-80. 

It is not easy to keep track of the rings when the system is 
exactly edge-on. Small telescopes will show no trace of the 
rings for a period of several weeks, but during 1966 T.J, G. A. 
Moseley, P. G. Corvan and myself, using the 10-inch refractor 
at Armagh Observatory, found that the rings could be seen as 
a thin and excessively faint line. I doubt whether any smaller 
telescope would have shown them at all between late October 
and the end of the year. 

Fig. 4 1 . Aspects of Saturn's Rings. One full cycle is shown; 
the rings are closed in positions 1, 5 and 9; the southern 
face of the ring is shown in 2-4, the northern face in 6-8. 



Saturn is an awkward object to draw, but there is no "short 
cut", as in the case of Jupiter. Stencils can be made to allow for 
the polar flattening of the disk, but the rings have to be sketched 
freehand. Unfortunately it is not possible to prepare one standard 
drawing and use it as an outline for weeks on end, as the presen- 
tation of the rings alters perceptibly even over short periods. 

Points to note are the intensities of the various rings (B is 
always brighter than A), the shadow effects of rings on disk and 
disk on rings, and the visibility of any of the Divisions. Occasion- 
ally Saturn occults a star, and these occultations are important, 
since even the bright rings are semi-transparent and the dim- 
ming of the star is a key to the composition of the rings. Ring 
C, the Crepe or Dusky Ring, has been suspected of variations in 

Saturn has ten satellites. Of these the largest is Titan, 3,600 
miles in diameter according to one estimate. It has an atmos- 
phere, made up chiefly of methane, and can be seen with a 
2-inch telescope. The magnitude is 8$, so that it is an easy 
object. Next in order of brilliancy come Iapetus and Rhea, 
which can be seen with a 3-inch refractor; Dione and Tethys 
are easy with a 4-inch. I have seen Enceladus, Mimas and 
(occasionally) Hyperion with my i2$-inch reflector ;Phcebe, the 
outermost satellite, is much fainter. It is a long way from Saturn, 
and moves in a retrograde or wrong-way direction, so that it is 
probably a captured asteroid. 

The amateur can do useful work in estimating the magnitudes 
of the satellites, since the published figures do not agree at all 
well. Field stars can be used when available — but make sure to 
identify both stars and satellites correctly ! Iapetus is of special 
interest, since it is much brighter when west of Saturn than 
when to the east. My estimates show that it can reach to above 
magnitude 9, though this is not the official view. Either Iapetus 
is irregular in shape, or else it has a surface of unequal reflec- 

There remains Janus, which was discovered in 1966 by 
Dollfus in France. It is the closest-in of the satellites, and is 
visible only when the rings are edge-on. I have to admit that I 
overlooked it completely. I had been making estimates of the 
inner satellites, and after Dollfus' discovery I found that I had 
recorded Janus on at least four occasions in the autumn of 1 966 



without realizing that it might be new — a good case of over- 
looking what was unexpected. 

Uranus, discovered by William Herschel in 1781, has a dia- 
meter of 29,300 miles. In spite of its great distance, never less 
than 1 ,600 million miles from the Earth, it can just be seen with- 
out a telescope; a small instrument will reveal its dim, greenish 
disk. Faint belts can sometimes be seen with apertures of ro 
inches and over, but little else can be made out. 

Uranus is a celestial oddity. Whereas most of the planets 
have their axes of rotation inclined to the perpendicular to the 
planes of their orbits by 20 or 30 degrees (Fig. 42), Uranus has 

Fig. 4a. Axial inclinations of the major planets. 

an inclination of more than a right angle. Consequently the 
"seasons" there must be most peculiar, particularly as the 
"year" is 84 times as long as ours. First much of the northern 
hemisphere, then much of the southern is plunged into darkness 
for 2i years at a time, with a corresponding period of daylight 
in the opposite hemisphere. Sometimes we look straight at the 
pole, as in 1945, while at others the equator is presented.* 
In itself, the planet appears to be rather different from Jupiter 
or Saturn, but the surface is wholly gaseous. 

Few amateurs will possess telescopes large enough for study- 
ing the surface of Uranus, but it is interesting to estimate the 
planet's brightness, since there seem to be irregular varia- 
tions which may be linked with disturbances on the disk. The 
method of estimation is to compare Uranus with a near-by star 
of known brilliancy, just as is done in the case of a variable 
star (see Chapter 15). 

A low power, 50 to 70 on a 3-inch refractor, is best for this 
work. With higher magnifications, Uranus appears as a definite 

• According to an old fairy story, the Earth's axis used to be upright, but the 
hideous crimes of mankind caused it to tUt to it* present angle of 33}=. In the case 
of Uranus, the tilt is 98", so that I hate to think what must have happened there! 



disk, and is difficult to compare with a star. In 1955, when 
Uranus and Jupiter lay close together in the sky, I tried to 
compare Uranus with Ganymede and Callisto, but the planet 
was so much larger and dimmer than the satellites that I was 
unable to get any reliable results. Observations of an occulta- 
tion of a star by Uranus in 1977 resulted in the detection of a 
system of rings, but these rings are much too faint to be seen 
directly. If Voyager 2 by-passes Uranus in 1986, we may 
obtain positive confirmation. 

Uranus has five satellites. Of these, Titania and Oberon 
should be visible with an 8- or 9-inch telescope; Ariel and 
Urabriel require at least 18 inches, and Miranda is beyond any 
but the world's largest instruments. Titania, the most easily 
detected member of the family, is about 1,500 miles across, so 
that it is appreciably smaller than our own Moon. 

Neptune, last of the giants, is the true twin of Uranus. It is 
similar in size, slightly more massive, and more distant, 
since even at its closest point to the Earth it is still 2,675 million 
miles away. It can be seen with any small telescope, but with 
anything less than 4 inches of aperture it looks very like a star. 
Larger instruments show a bluish disk, practically devoid of 

The story of Neptune's discovery is one of the most interest- 
ing in astronomical history, since the planet was tracked down 
before it was actually seen. Between 1781 and 1830, mathe- 
maticians found that the new planet Uranus was wandering 
from its predicted path; it was not moving as it should do, and 
an amateur, the Rev. T. J. Hussey, suggested that the cause of 
the trouble might be an unknown body, pulling on Uranus and 
dragging it slightly away from its expected position. Two 
investigators, John Couch Adams in England and Urbain Le 
Verrier in France, set themselves to work out the position of the 
disturbing body. It was a true detective problem ; they knew the 
victim, and they had to find the culprit. 

Adams finished first, and sent his calculations to the then 
Astronomer Royal, Sir George Airy. Unfortunately Airy took 
no immediate action, and by the time he did give orders for a 
search it was too late ; Le Verrier's results enabled two German 
astronomers, GaUe and D'Arrest, to identify the new world 
very close to the position that had been indicated. 



Neptune does not share Uranus' great axial tilt, and al- 
though it is satisfying to find the remote, frigid giant, there is 
little scope for the amateur. However, a 6-inch telescope should 
show the major satellite, Triton, which is brighter than any 
of the moons of Uranus, and was discovered shortly after 
Neptune itself had been recognized. The second satellite, 
Nereid, is excessively faint. 

With the discovery of Neptune, the Solar System was once 
more regarded as complete. Yet the movements of the outer 
planets were still not in full agreement with calculation; and 
Percival Lowell, famed for his studies of the Martian canals, 
undertook to work out the position of a ninth planet. 

The problem was much the same as that which had con- 
fronted Adams and Le Verrier, but was even more difficult, and 
Lowell had no success. He died in 1916, but the search was 
continued at his observatory, and fourteen years later Clyde 
Tombaugh detected a dim, starlike object which proved to be 
the missing planet. It was christened Pluto, and the name is 
apt; Pluto was King of Darkness, and the world named after 
him must be a dismal, twilight place, with the Sun looking 
like nothing more than a tiny though intensely brilliant disk. 

Pluto has set astronomers problem after problem. The 
most annoying thing about it is its size. It is much smaller 
than Lowell had anticipated, and it seems indeed to be no 
larger than Mars, so that it is a solid body and not a gaseous 
globe. It cannot have a strong gravitational pull, and unless 
something is badly wrong with the measurements it can have no 
detectable effects upon the movements of Uranus or Neptune 
— yet it was by these very effects that Pluto was tracked 

It is hard to believe that Lowell's accuracy was due to sheer 
luck, particularly as independent work by another American 
mathematician, W. H. Pickering, gave a similar result. It has 
been suggested that Pluto is really larger than the measures 
indicate, but at present the puzzle remains unsolved. 

We know little about Pluto itself. Researches carried out 
in 1956 yield a rotation period of 6 days 9 hours, but the 
planet is so small and so far away that no ordinary telescope 
will show its disk. 

The orbit is strange, and quite unlike that of any other major 



planet. The sidereal period is 248 years, and the distance 
from the Sun varies from 2,766 million miles at perihelion to as 
much as 4,566 million at aphelion. At its closest to the Sun, 
Pluto is actually closer-in than Neptune, but the orbit is appre- 
ciably tilted, so that there is no fear of the two planets meeting 
in collision — though there is a possibility that Pluto is a former 
satellite of Neptune that has broken loose, and is now masquer- 
ading as a planet in its own right. 

Pluto is drawing in to perihelion, and it has brightened up 
considerably since its discovery. It will go on increasing in 
brilliancy until it passes perihelion in 1989. A 12-inch telescope 
will now show it, and it can be identified in the same way as an 
asteroid, though with more difficulty on account of its slower 
motion. Fig. 43 shows its orbit. It is worth while making a 
search for Pluto just for the satisfaction of seeing it. 

The main problem of Pluto concerns its size. Of all the 
world's telescopes, only the Palomar 200-inch will show a per- 
ceptible disk, and perhaps the main hope lies in an occultation 
of a star by the planet; the duration of the occultation would 

Fig. 43. The orbit of Pluto. Perihelion — 1989; 
aphelion — a 1 1 3. 



provide a clue to the apparent diameter. This method has 
already been applied in the case of Neptune and some of 
Jupiter's main satellites, mainly by G. E. Taylor of the 
Royal Greenwich Observatory, Herstmonceux. Unfortunately 
occultations by the slow-moving Pluto are very rare, and as yet 
no such phenomenon has been observed. Moreover, a large 
telescope, used together with photoelectric equipment, would 
be needed to give any worth-while results. 

Is there another planet beyond Pluto? There may well be, 
but if so it will be so dim that we may never find it. So far as 
we can tell at present, Pluto marks the frontier of the Sun's 
inner kingdom. 

Enough has been said to show that any amateur with 
energy and patience can do valuable work in the field of 
planetary observation. He may not have a large telescope; he 
may not possess a scientific degree, but at least he can make 
himself useful if he wants to. And after a lifetime's work, he 
will realize that there is still much that he has left undone. 

During the coming years we should learn much more from 
probes sent to the outer planets. Pioneers 10 and 1 1 showed the 
way; Pioneer n is now en route for Saturn, while the two 
Voyagers launched in 1977 should by-pass Jupiter in 1979 and 
then encounter Saturn in 1980 and 1981 respectively. If all 
goes well, Voyager 2 may even by-pass Uranus (ig86) and 
Neptune {1989 or 1990). Anything of the kind would have 
seemed inconceivable a few decades ago, but there now seems 
every hope that by the end of the century we will have obtained 
close-range photographs of all the giant planets. They are 
fascinating worlds, if only because they are so utterly different 
from our own Earth. 


Chapter Eleven 


A brilliant comet, with a tail that stretches half-way 
across the sky, is one of Nature's greatest spectacles. Small 
wonder that it caused fear and panic in ancient times, when 
comets were believed to be heralds of disaster, Shakespeare 
wrote in Julius Casari 

"When beggars die, there are no comets seen: 
The heavens themselves blaze forth the death of princes," 

and even to-day the feeling is not entirely dead. Yet there is 
not the slightest foundation for it, since comets are the flimsiest 
and most harmless members of the whole Solar System. 

Broadly speaking, a comet is made up of small pieces of 
matter, ranging in size from sand-grains to blocks bigger than 
houses, enveloped in thin gas. A comet is not therefore a hard, 
solid body like a planet, and even the largest comet has a mass 
smaller than that of a minor satellite such as Phoebe. 

A few people still confuse comets with meteors, or shooting- 
stars. There is of course a link between the two, as will be shown 
below, but there is no excuse for any misunderstanding. 
Whereas a shooting-star is a piece of matter that dashes into the 
air, perishing in a streak of radiance after a few seconds, a 
comet may remain visible for months, moving so slowly against 
the starry background that its motion cannot be detected 
except over a period of some hours. 

The popular idea of a comet is of a vast fuzzy mass with a 
magnificent tail streaming out of it. Great comets do in fact 
look like this, and are made up of three main parts known as 
the nucleus or central condensation, the coma and the tail, 
but smaller specimens are much less imposing. I remember 
showing a telescopic comet to a friend of mine who knew little 
about astronomy and cared less. His comment was that the 
comet looked "like a small lump of cotton- wool", and there 
was some truth in the description. 

The coma or head of a comet looks like a filmy mass, and is 



made up chiefly of tenuous gas enveloping scattered pieces of 
meteoric matter. Near the middle of the coma there may be a 
central condensation, so sharply denned that it looks like a star, 
and in which the solid particles are more numerous and more 
closely packed. If there is a tail, it streams away from the coma, 
merging into it so perfectly that it is usually impossible to tell 
where the one begins and the other leaves off. The gas compos- 
ing the tail is so thin that its density is negligible according to 
our normal standards, but here too there is plenty of dust.* 


Fig. 44. Direction of a comet's tail with respect to the Sun. 

The nucleus or central condensation seems to be the most 
important part of any comet, and it is assumed that the coma 
and tail are formed by gases given off by the matter in the 
nucleus when heated by the Sun. It is significant that most 
comets develop tails only when near perihelion, and lose them 
again when they have receded some way after perihelion 
passage; but there are of course exceptions to the general rule, 
and we have to admit that the mechanism of tail formation is 
still not properly understood. 

One curious fact is that the tail always points away from 
the Sun. When the comet is racing towards perihelion it travels 
head-first in the conventional way, but after passing perihelion 
it moves tail-first (Fig. 44). The tail must whirl round at a 
tremendous speed during the passing of perihelion, and in some 
cases the old tail disappears, to be replaced by a new one on the 
far side of the comet. 

• "Dust" must not be taken to mean the sort of dust that one finds on the 
mantelpiece in a disused room. The particles in a comet may be mainly ices, as 
was suggested by F. L. Whipple in 1950, 


This interesting behaviour was formerly explained as being 
due to the fact that light exerts a pressure; it was thought that 
with the small particles making up a comet's tail, light- 
pressure was able to drive the material outward. It has now 
been found that this explanation is inadequate, and that the 
phenomenon is better accounted for by introducing magnetic 
effects together with particles sent out by the Sun, though 
further researches are in progress. At any rate, a comet must be 
subject to a steady wastage of material, and on the cosmieal 
time-scale it is a short-lived body. 

Most of the periodical comets of short period are too faint 
to be seen without a telescope, even when at their brightest, 
and when far from perihelion they cannot be seen at all. We 
speak of the "return" of a comet when it comes back to the 
regions in which it can be observed. Encke's Comet, for in- 
stance, has a period of 3.3 years; it has now been observed at 
over fifty returns, the latest being that of 1978. It is so named 
because the German mathematician Encke was the first to 
realize that it revolves round the Sun, and that in consequence 
its returns can be predicted. Its orbit is shown in Fig. 45. 

Over 30 known short-period comets, including Encke's, 
have their aphelion points at or near the orbit of Jupiter. 
They form a sort of family, and clearly the Giant Planet is 
concerned in some way. It is not suggested that comets are 
formed from Jupiter or by Jupiter, but the powerful gravita- 
tional pull exerts some control on their movements. By the 
beginning of 1978 there were about 100 comets known to have 
periods of less than 200 years, but most of them are extremely 
faint, so that large telescopes are needed to show them. 

The chief exception is, of course, Halley's Comet, which 
comes back every 76 years. It is the only comet of short or 
moderate period which can be called "great", and it is a 
majestic spectacle for a few months at each apparition. It is 
named after the second Astronomer Royal, Edmond Halley, 
who is closely linked with its history. 

In 1682 a bright comet appeared, and was observed by 
Halley. He worked out its orbit, and found that it moved 
strangely like other comets previously seen in 1607 and in 
1 53 1. Halley realized that the three bodies must in fact be 
different returns of the same comet, and he predicted that it 



would be seen again in 1758. Though he did not live to see 
the vindication of his prophecy, the comet was duly picked up 
on Christmas Night by a German amateur using a 6-inch 
telescope, and it actually passed perihelion on March 12, 


Fig. 45. Orbit of Encke's Comet. 

1759, after which it vanished until the return of 1835. It was 
seen once more in 1910, and is due back in 1986. It was Halley's 
Comet, too, that shone down on Saxon England in the early 
part of that most "memorable" year, 1066, and there arc 
records of it that go back to before the time of Christ. 

At present (1978), Halley's Comet lies outside the orbit of 
Saturn, and it is interesting to see what will happen to it in 
future years. The first thing shown from Fig. 46 is that the 
motion is retrograde, so that it is moving "the wrong way 
along a one-way street" in the same manner as Phcebe and the 
four outer raoonlets of Jupiter. In 1948 it reached aphelion, 



and started to draw back slowly towards the Sun, crossing the 
mean path of Neptune in 1967. Another 10 years brought it 
as close as Uranus, but after 1980 it will be moving so much 
more rapidly that it will cover the rest of the distance to 


Fig. 46. Orbit of Halley's Comet. Aphelion— 1948; perihelion— 


perihelion in only another 6 years. By 1987 it will have receded 
once more beyond Jupiter, and unless we have by then com- 
pleted more powerful telescopes we shall lose sight of it for 
another three-quarters of a century. 

Unfortunately no other comet of reasonably short period can 
compare with Halley's, and most are faint telescopic objects, 
generally with tails that are either very faint or else absent alto- 
gether. One or two comets have peculiar orbits, a good example 
being known by the cumbersome name of Schwassmann- 
Wachmannl. Here the orbit lies entirely between those of Jupi- 
ter and Saturn, and is comparatively circular, so that the comet 



can be observed at any time when conditions are favourable. It 
is usually very faint, but sometimes brightens up considerably, 
so that it is a worth-while object for observers equipped with 
large telescopes. 

Since four or five new comets arc discovered every year, 
some of them genuinely new discoveries and others mere 
returns of old friends, some system of naming is essential. 
There are two systems, one temporary and the other permanent. 
In the first, the year's comets are allotted a letter in order of 
discovery (a, b, c, d, etc.) ; in the second, a comet is given a 
Roman numeral according to its order in passing perihelion, 
A comet that was the second to be discovered in 1 972, but the 
fourth to pass perihelion in 1972, would become first 1972 b and 
then 1 972 IV. Of course, there is no guarantee that a comet 
will reach perihelion in the year of its discovery; 1978 m or n 
may become 1979 II or III. 

The names of the discoverers are often used. Two inde- 
pendent discoverers may be bracketed together, as in the case of 
Schwassmann and Wachmann, while on rarer occasions it is 
resolved to name the comet after the mathematician who 
computes its orbit. This was done in the case of Halley's and 
Encke's Comets, and a more recent example is Grommelin's 
Comet, which can just be seen without a telescope at a favour- 
able return, and has a period of 28 years. The late A. C. D. 
Crommelin, a well-known expert on the subject, discovered 
that comets seen at different returns by Pons, Coggia, Winnecke 
and Forbes were identical. It was obviously just to attach 
Grommelin's name to it rather than to retain the names of all 
four discoverers. 

Not all comets are periodic. Some have orbits which are 
almost parabolic (open curves} (Fig. 47), so that after having 
passed perihelion they retreat into space, never to return. 
There is little obvious difference between an open curve and a 
very long ellipse, and there are many comets which have 
periods of such length that they will not be seen again for 
generations. For instance, Quenisset's Comet of 191 1 has an 
estimated period of over 9,000 years, and if this figure is 
accepted the modern return was the first since the end of 
the last Ice Age. Comet 1902 III seems to have a period of 
over a million years. It must be stressed, however, that periods 



Fig. 47. Open curves; parabola and 


of this kind are qune unreliable, and all we can say with 
certainty is that the periods of such comets are extremely long. 

It used to be thought that comets with open or apparently 
parabolic orbits came from space, visited the Sun once, and 
returned to interstellar space. This is not now believed to 
be the case. Comets are 
insubstantial bodies, at 
the mercy of the planets, 
so that their orbits may 
at any time be violendy 
perturbed, and the re- 
sults arc sometimes re- 
markable. Jupiter, ow- 
ing to its tremendous 
mass, has the greatest 

Apart from Halley's, 
most great comets are either non-periodical or else have 
periods of hundreds of years. Several were seen during the 
nineteenth century, but between 1910 and 1978 there was a 
relative dearth of them. There were of course, comets visible 
without telescopic aid, but faint objects at the limit of naked- 
eye visibility are very different from the spectacular Great 
Comets of the past. The comet of 1843 had a tail which 
stretched right across the sky, while that of 1858 (Donati's) 
was peculiarly beautiful in view of its triple tail, curved like a 
scimitar. Another particularly brilliant comet was seen in 

One of the most interesting comets of recent times was Arend- 
Roland, discovered in November 1956 by the two Belgian 
astronomers after whom it was named. Though hardly a "great 
comet" in the true sense of the word, it was a conspicuous 
naked-eye object for a short time in April 1957. On the 27th 
of that month, I had a particularly good view of it in the late 
evening ; the nucleus lay close to the star Alpha Pcrsei, and the 
long tail extended upwards from the horizon, so that it was a 
splendid sight in binoculars or a low-power telescope (to me, 
it seemed most impressive with binoculars). One of the inter- 
esting features of this comet was a curious "reverse tail". 
This "reverse tail" was still faintly visible on April 27, and is 



shown in Plate XI, while the nucleus of the comet then appeared 
almost stellar. 

There have been various comets which have become bright 
enough to be conspicuous. One was Ikeya-Seki, discovered by 
two Japanese astronomers in the summer of 1965. From Europe 
it was disappointing, though good views of it were obtained 
from the United States. Bennett's Comet of 1969, discovered by 
the South African amateur Jack Bennett (one of the most 
skilled comet-hunters in the world) did achieve prominence, 
and developed a long tail. But the main disappointment was 
Kohoutek's Comet of 1973, which was expected to become 
really spectacular, but which signally failed to do so. 

When discovered, by Dr. Lubos Kohoutek at the Hamburg 
Observatory, it was very faint, but it was also a very long way 
from the Sun, and early predictions indicated that towards the 
end of the year it might exceed magnitude - 10. Alas, it did not 
brighten up as had been hoped, and although it was visible 
with the naked eye it was by no means spectacular — certainly 
inferior to Bennett's Comet of four years earlier. However, it was 
interesting scientifically, and was found to be associated with a 
vast cloud of tenuous hydrogen ; it was studied by the last crew 
of America's space-station Skylab, and a great deal was learned 
from it. The estimated period is 75,000 years, so that it will not 
come back in our time. 

West's Comet of 1975 was brighter, and almost qualified for 
the title of "great". Over Britain it made a brave showing in the 
dawn sky for several mornings in succession. During its flight 
round the Sun it showed obvious signs of disintegration, so that 
when it next returns — in many centuries from now — it will have 
none of its twentieth-century glory. 

It is a great pity that brilliant comets have been in such short 
supply lately. Indeed, the last really spectacular visitor was 
the "Daylight Comet" of 19 10 (which is not periodical, and 
should not be confused with Halley's, which returned in the 
same year) . Of course, there is no knowing when another great 
comet will appear. It could happen at any time. 

When a short-period comet is due to return, its expected 
position at the time of anticipated recovery is given in a yearly 
publication such as the B.A.A. Handbook. The positions given 
are usually accurate enough for quick identification. Last time 



Encke's Comet came round, I picked it up without difficulty as 
soon as it came within range of my portable 3-inch refractor; 
and I am not, and never have been, a regular observer of 


The chief scope from the amateur's point of view is that many 
comets appear unexpectedly, and completely "out of the blue". 
There is always the chance of making a discovery, and some 
amateurs are adept at it, so that they have established inter- 
national reputations. 

Comet-sweeping is therefore a worth-while occupation, 
but the beginner must resign himself to many disappointments 
and many hours of fruitless searching. He may not discover a 
comet for years, or he may never discover one at all. There is 
however a great consolation, since even if he fails to find a 
comet he will be certain to come across many stellar objects of 
real interest. 

Never use a high magnification. What is needed is a large 
field of view, and in any case a powerful eyepiece is of little 
use upon a badly-defined, fuzzy object such as the average 
comet. Binoculars are also suitable— provided that they are 
properly mounted, and are large enough to collect an adequate 
amount of light. 

Having selected the region to be swept, the telescope is 
moved slowly along in a horizontal direction (if on an altazi- 
muth mount), with the observer keeping a careful watch all 
the time. Stars, clusters and other objects will creep through the 
field, and the slightest relaxation of attention may mean that a 
vital comet is missed. At the end of the sweep the telescope is 
raised or lowered very slightly, and an overlapping sweep 
taken in the opposite direction. After this process has been 
carried on until the whole area has been covered, it should be 
repeated several times until the watcher is satisfied that no dim, 
misty object can have escaped him. 

Much patience b called for, and things are made more 
difficult by the presence of star-clusters and nebula, which 
look very much like comets. The name "star-cluster" speaks for 
itself, while a "nebula" is rather similar in appearance, and is 
made up either of stars or of gas. If you are sweeping the 
heavens in search of a comet, and happen to find a misty 
object that is certainly not a star, it is unwise to jump to any 

■ 145 


conclusions. Reference to an atlas will probably show that the 
object is a cluster or a nebula that has been known for 

There is an interesting story about these clusters and nebulae. 
Charles Messier, a famous comet-hunter of the eighteenth 
century, was persistently misled by uncharted stellar objects, and 
eventually he drew up a catalogue of "objects to avoid", rather 
as a navigator charts shoals in a strait. Nowadays Messier's 
comets are forgotten by all but a few enthusiasts, while his 
catalogue of clusters and nebula remains the standard. 
Messier himself would undoubtedly have seen the irony of the 

Many comets will lie somewhere near the Sun's line of sight 
when they are approaching perihelion, and nearly all remain 
undiscovered until they arc well within the orbit of Mars, 
particularly as the average comet brightens up considerably 
as it draws near the Sun and the heat acts upon the particles 
in the nucleus. Consequently, the most promising areas of the 
sky for sweeping, for an observer in the northern hemisphere, 
are the west and north-west after sunset and the east and north- 
east before sunrise. It is also worth sweeping in the low north. 
It is no use beginning until the sky is really dark, since a faint 
comet will be drowned by any background light. 

Though more new comets will be seen in these directions 
than in others, there is no hard and fast rule. A comet may 
appear at any moment from any direction; it may have an 
open or a closed orbit, it may be highly inclined, it may be 
moving in a retrograde or wrong-way direction. Comets have 
been called the stray members of the Solar System. Flimsy, 
harmless and of negligible mass, they can do harm to nobody. 
Moreover, they are short-lived upon the astronomical time- 
scale, and several short-period comets seen at several returns 
during the past have now vanished for good. Such are the 
comets of Biela and Brorsen. 

Apart from comet sweeping, the amateur who has equipped 
himself with an equatorial mount, a measuring device and 
perhaps a camera, can do valuable work in checking the 

^ * Odd things have happened now and again. Not long ago, one observer reported 
a "comet" that proved to be merely a reflection in his telescope, and there have been 
other similar cases. Even better was the "discovery" of a bright red star in the 
constellation of the Bull, not far from Aldcbaran. It turned out to be Mats. 



positions of comets from night to night. Mathematically- 
minded workers may prefer to make a hobby of computing 
orbits. This is not an easy process, and real skill is needed, but 
anyone who has the necessary ability and patience will soon 
find that his services are in great demand — more especially if 
he is the owner of a computing machine ! 

The link between cometary and meteoric astronomy is 
perhaps shown most clearly by the interesting case of Biela's 
Comet, whose peculiar career caused many astronomers many 
sleepless nights. The comet was discovered by Biela, an Austrian 
astronomer, in 1826, and found to be identical with comets 
previously observed in 1772 and in 1805. It was one of Jupiter's 
short-period group, and had a period of about 6| years. It 
returned in 1832 as predicted, was missed in 1839 owing to its 
unfavourable position in the sky, and returned once more in 

Up to then, the comet had behaved in a perfectly normal 
manner, but during the return of 1845-46 it astonished ob- 
servers by splitting into two pieces. Where there had been one 
comet, twins could be seen, sometimes with a kind of filmy 
bridge between them. Sometimes the two were nearly equal, 
sometimes the original comet was the brighter. Both faded 
gradually into the distance, and the return of 1852 was eagerly 
awaited. This time the two comets were farther apart, the 
second following the first rather like a child following its 
mother. At the 1859 return conditions were again hopelessly 
bad, but in 1856-66 the comet should have been an easy 
telescopic object. Yet it was searched for in vain. There was no 
trace of it; so far as could be made out, Biela's Comet had 
disappeared from the Solar System. Comets have been nick- 
named "ghosts of space", but no ghost could possibly have done 
a more successiul vanishing act. 

The next return should have taken place in 1872. Again the 
comet was absent, but in its place appeared a rich shower of 
meteors. Coincidence can be ruled out, and for years after- 
wards meteors were seen each year at the time when the 
Earth crossed the path of the dead comet. This shower is still 
active about November 28 annually, though it has now 
become very feeble. 

It would be misleading to say simply that Biela's Comet 



"broke up" into meteors. There is more in it than this, and the 
position has been made clearer by the associations of other 
comets with other meteor showers; HaUey's Comet, for 
instance, is linked with the meteor shower seen each year during 
the first week in May, and known as the Aquarids. Debris must 
be spread widely along the track of a comet, though once 
again it would be misleading to suppose that all meteors must be 
connected with comets. 

Most people have wild ideas about the sizes of the particles 
which become incandescent and are rapidly burned up to 
become shooting-stars. Actually, the particles are very small. 
A body the size of a grape would produce a brilliant fireball, 
while the average bright meteor is due to a particle less than a 
tenth of an inch in diameter. like comets, meteors are less 
important than they seem. 

A meteor travels round the Sun in an elliptical orbit, some- 
times as a member of a shoal ("shower meteor") or as a lone 
wolf ("sporadic meteor"). If it comes close to the Earth, and is 
moving in a suitable fashion, it may enter the upper atmosphere 
at a relative speed of up to 45 miles per second. Below an 
altitude of 1 20 miles or so, there is enough air to cause appreci- 
able resistance; heat and visual radiation are generated, and 
the hapless meteor is generally destroyed, ending its journey in 
the form of fine dust. Millions of shooting-stars enter the 
Earth's atmosphere every day. Most are smaller than grains of 
sand; the so-called micro-meteorites, which have been investi- 
gated recently by means of sending high-altitude rockets above 
the densest layers of the atmosphere, seem to have diameters of 
something Eke 5/1000 of an inch, and may be similar to the 
particles which cause the glow of the Zodiacal Light. 

Sporadic meteors may appear from anywhere at any time, 
but shower meteors are more obliging. If the Earth passes 
through an area in space which is rich in meteors, the ordinary 
laws of perspective will cause the meteors to appear to radiate 
from one point. This is shown in Fig. 48, where all the meteors 
appear to converge towards a distant point P, which can be 
regarded as the apparent "radiant" of the meteors. 

A meteor shower is named according to the constellation 
in which the radiant seems to he. For instance, one major 
shower visible each November has its radiant in Leo, the Lion, 



and is thus called the Leonid Shower; of course, this does not 
mean that all the meteors appear near Leo, but merely that if 
the paths were plotted back, they would converge to a small 
area in Leo known as the radiant. Similar, the October 
Orionids radiate from Orion, and the August Perseids from 

Some of the annual showers are more important than others, 
and a list is given in Appendix XIV, but really spectacular 
displays are very rare. Such were the showers of 1833 and 1866, 
when the Leonids (associated with Tempel's periodical comet) 
were much more numerous than usual, and it was said that 
shooting-stars seemed to "rain down like snowflakes". 

In fact, the Leonids had had a long and spectacular history, 
and had been consistent in providing major displays every 33 
years. After 1866, the next was due in 1899— but by then, 
unfortunately, the meteor swarm had been affected by 
planetary perturbations, and the main cluster missed the Earth, 
so that the expected display did not materialize. The next 
return was due in 1933 (not 1932), but again there was nothing 
of note. 

Conditions seemed more promising for 1966. The Leomd 
displays of 1963 and 1964 showed an encouraging increase, 
and this was also true of 1965, though for that year the 
observations were hampered by the inconvenient presence of 
the fuU moon. Much was hoped for 1966, and earlier in the 
month I put out a television appeal for what is known officially 
as "audience participation". With me was H. B. Ridley, the 
Director of the Meteor Section of the British Astronomical 
Association. We announced that charts and 'answer cards' 
would be distributed, and during the next few days the B.B.C. 
dispatched more than 10,000 of these charts and cards to people 
who wrote in for them. 

The result was a sad anti-climax. In Ireland, where I was 
observing, the skies were reasonably clear, but at an early 
stage it became evident that the Leonids were going to fail 
us yet again. We saw some meteors, and plotted a radiant, 
but the display was so poor that nobody would have noticed 
it except by careful, systematic watching. Matters were 
very different elsewhere. As seen from parts of the United 
States (Arizona, for instance) the hourly Leonid rate reached 



100,000 — it was the greatest display of the century. Maximum 
occurred at about 12 hours G.M.T., while it was daylight in 
Europe; in fact, British observers missed the display by six 
hours. Yet the counts made by British amateurs were valu- 
able scientifically, 

The fact that the display was so brief proved that the 
meteors were "bunched" together, and were not spread all 
along the orbit of their parent comet in the same manner as 
the Perseids. Unfortunately we cannot expect another specta- 
cular Leonid shower for 
some time, though ob- 
servers will certainly be 
on watch during the 
period around 1999. 

To find out the speed, 
height and orbit of a 
meteor, three data must 
be provided: the point 
of appearance of the 
meteor, the point of dis- 
appearance, and the 
duration. Clearly it is 
necessary for the same 
meteor to be observed 
by two workers placed 
at least twenty miles 
apart (more if possible). 
A single observer cannot 
do much if he has to 
depend only upon his 
own labours. 

No instruments are needed for meteor recording, but the ob- 
server has to have a really good knowledge of the constellations, 
as otherwise he will be unable to plot the track. The track 
must be plotted on a star map, but it is unwise to look down as 
soon as the meteor has vanished and try to record where it 
went, since errors are certain to creep in. The solution is to 
check the path by holding up a rod or stick along the track 
where the meteor passed, which will give you the chance to 
take stock of the background and ensure that no mistake has 


Fig. 48. Diagram to illustrate the 
principle of a meteor radiant. 
The meteors are assumed to be 
parallel, but to the observer the 
paths will seem to diverge from 
the point P. 


been made. When you are satisfied, either draw the path on 
your chart or note the exact positions of the beginning and end 
of the track, and then write down: time of start, duration, 
duration of luminous trail, brightness (compared with that of 
a known star or stars), colour (if any), and any special features. 
Meteor watching is a lengthy and often a cold business. 
Standing out for hours during a January or February night is 
enough to chill the enthusiasm of the hardiest observer. Never- 
theless, until recently all researches were based upon the 
patient work of amateurs, among whom the name of W. F. 
Denning will always be remembered. It is fair to say "until 
recently", because in 1946 an entirely new method of recording 
was brought into operation, that of radar. 

The passage of a meteor through the atmosphere has a 
pronounced effect upon the air-particles, and these effects can 
be detected by radar. Reduced to its barest terms, radar 
involves sending out an energy wave, and recording the echo 
as the wave is bounced back after hitting a solid object. A 
meteor trail is not of course a hard body, but it acts just as 
violently, and radar detection of shooting stars has now been in 
progress for some time. The method is unhampered by clouds 
or daylight, and it would be idle to pretend that it has not 
affected the value of amateur visual work, though the naked- 
eye watcher can still make himself useful. 

Casual meteors are fairly frequent, and a watchful observer 
will seldom fail to record fewer than five or six per hour, but 
it is of course far more entertaining (though not necessarily 
more useful) to concentrate upon some definite shower. 
Occasionally there will be so many meteors in quick succession 
that the watcher will be hard pressed to record them all, but 
this will not happen often, and there must be long periods of 
patient waiting. 

It is interesting to note that visual meteors are twice as 
abundant in the period from midnight to 6 a.m. as during the 
period from 6 p.m. to midnight. In the evening, we are on the 
"rear" of the Earth as it moves in its orbit, so that visible 
meteors have to catch us up ; in the morning hours we are in the 
"front" position, so that meteors meet us coining. More meteors 
are to be expected after midnight than before it, and obviously 
the morning meteors will have greater relative speed, just as a 



car moving at 30 m.p.h. and meeting a second car moving at 
35 m.p.h. will be badly damaged if the collision is head-on, 
but only bumped if rammed from behind. It is the relative 
speed of a meteor which is the main factor in its brightness, so 
that the morning meteors will be more brilliant and hence easier 
to record. 

Though meteors and comets are so unpredictable, at least 
when compared with the planets, studies of them are full of 
interest. Moreover, there is always the chance of making a 
spectacular discovery or discoveries — as happened to a British 
amateur, G. E. D. Alcock, in 1959, when he found two new 
comets in quick succession. On the other hand, the amateur 
who wishes to make a serious, useful study of meteors is more 
likely to concentrate upon photographic work; there is a 
great deal to be done, for instance, in photographic recording 
of meteor spectra. Many hours of exposure are needed to 
capture even one meteor spectrum, but a successful photo- 
graph is of great value. One of the pioneers in this field is 
H. B. Ridley, who, like Alcock, is an amateur. 

Larger bodies, more nearly related to the asteroids than to 
ordinary meteors, survive the complete drop to the ground, and 
are known as meteorites. Most museums have collections of 
them, and an expert can soon tell what is meteoritic material 
and what is not, though the layman is easily misled. In general, 
meteorites are divided into two classes, stones (aerolites) and 
irons (siderites). 

Large meteorites are rare. The biggest of modern times fell 
on June 30, 1908, and landed in Siberia, blowing pine-trees 
flat for 50 miles all round the impact point; there must have 
been many earlier falls — witness, for instance, the large crater 
in the Arizona Desert, which is undoubtedly due to a prehistoric 
meteorite impact. Luckily, the dangers to human life are so 
slight as to be negligible. 

The last really interesting fall occurred in England on Christ- 
mas Eve, 1965. A meteorite flashed across the Midlands, 
attracting considerable attention, and broke up; fragments of 
it came down at Barwell, in Leicestershire. (I even found one 
myself when I visited the site some time later.) The original 
weight of the meteorite must have been about 200 pounds, 
which is a British record. One fragment went through the 


I. Telescopes 

(Left) Henry Brimon's 1 2-in. reflector at Selsey, 
Sussex. This ha* a skeleton tube, with rota- 
table head, and is equatnrially mounted, with 
an electric clock-drive. The mounting is of 
the so-called German type, with the weight 
of the telescope tube balanced by a counter- 
weight — or, in this instance, several counter- 

(Right) Patrick Moore's t z J-in. reflector former- 
ly at East Crinstead. Here the tube is solid, and 
the mounting is altazimuth, with manual slow 
motions, The telescope is of short focal length 
(72 in.) and is very easy to operate, but the 
need for constant adjustment is of course a 
serious handicap. 

ILefi) The rotatable head of 
I lenry Hrinlon's reflector. 
The entire head can be 
moved round, so that the 
eyepiece can always be 
brought into a position con- 
venient for viewing. This is 
a great advantage in view of 
the type of mount of the 
telescope; if the head did 
not rotate, things could 
become very difficult. 

1 1 . Observatories 

i Above) J. Hedley Robin- 
son's observatories al Tcign- 
mouth. The dome houses a 
10-in. reflector; the entire 
building: revolves. The run- 
i>iT shed houses a 3-75-111. 
equatorial refractor, 

(Right) Patrick Moure's ob- 
servatory at East Grinsfead. 
The upper part of the dome 
revolves. The observatory 
houses an 8j-in, equatorial, 
clock-driven reflector. It has 
now been transferred to 

■ mum m 


window of a house in BarweU, and was found later nestling 
comfortably in a vase of artificial flowers. 

Since then there has been the Bovedy Meteorite, which shot 
across England and Wales and dropped fragments in Northern 
Ireland. It attracted a great deal of attention, and produced the 
usual crop of flying saucer reports. I have to admit that I missed 
it by two minutes. I had been in my observatory at Selsey, 
observing variable stars, and had just gone indoors to change 
my charts when the meteorite passed over ! 

It is fitting to end this brief survey of the Solar System with 
the meteors and meteorites, its most insignificant members. We 
have described the Sun, the Moon, the planets and their satel- 
lites, the vivid glow of the aurora and the pale radiance of the 
Zodiacal Light, and the flimsy and unpredictable comets, so 
that there is variety in plenty; but even the Sun itself is a very 
junior member of the Galaxy, and we must keep our sense of 

Though the amateur's greatest scope is with the bodies of the 
Solar System, and many stellar problems cannot be tackled 
without using complex equipment, it would be a mistake to 
confine ourselves only to the Sun's family. Greater problems 
remain to be studied, and in any case a knowledge of the stellar 
universe can give one endless enjoyment. We must remember 
Carlyle's lament: "Why did not somebody teach me the 
constellations, and make me at home in the starry heavens?" 


(Above) Patrick Moore's run -off observatory al Sabey, 

Chapter Twelve 


When men of ancient times looked up into a starlit sky, 
they could see many hundreds of tiny, twinkling points that 
seemed to be arranged in definite patterns. It was natural, then, 
for the stars to be grouped into definite "constellations", each 
named after a deity, a demigod or else some common object. 
Orion the Hunter, Hercules of legendary strength, and Perseus 
with the Gorgon's Head mingle with the Dragon, the Fishes and 
the Cup. Forty-eight separate constellations are listed in the 
great catalogue contained in Ptolemy's Almagest, and may 
therefore be said to date from the dawn of astronomy. 

The names are generally used in their Latin forms, so that 
the Dragon is "Draco" and the Fishes "Pisces". Any amateur 
who means to do serious work in the field of stellar research 
should become accustomed to the Latin names, which are in 
any case easy to remember. A full list, with the English equi- 
valents, is given in Appendix XV. 

Ptolemy's 48 constellations are still used to-day, but others 
have been added since. Some of these new groups lie near the 
south celestial pole, so that they never rise in the latitude of 
Alexandria, and Ptolemy naturally knew nothing about them; 
others have been formed by taking pieces away from the 
original 48. Further proposed additions with barbarous names 
such as Sceptrum Brandenburgicum, Officina Typographica 
and Lochium Funis have been mercifully forgotten, though 
one of the rejected groups, Quadrans Muralis (the Mural 
Quadrant) has left a legacy in the form of the name of the 
annual Quadrantid meteor shower seen each year from January 
3 to 5. 

Probably the most famous of the constellations are Ursa 
Major {the Great Bear), Orion, and Crux Australis (the 
Southern Cross). Of these, Ursa Major lies in the far north 
of the sky, so that in England it never sets, while Orion is 
crossed by the celestial equator and Crux is so far south that it 
never rises in our latitudes. Stars which never set are termed 



"circumpolar", so that Ursa Major is circumpolar in England. 

To give a full explanation of the apparent movement of the 
star-sphere would be rather beyond our present scope, but 
something must be said about the essential terms Right 
Ascension and Declination. Broadly speaking, these are the 
celestial equivalents of longitude and latitude on the Earth's 
surface, though there are certain important differences in 

Declination is reckoned in degrees north or south of the 
celestial equator, while the equator itself is merely the pro- 
jection of the Earth's equator in the sky. Clearly the north 
celestial pole will have declination 90 degrees north (+90°), 
and Polaris, the Pole Star, with its declination of greater than 
-4-89°, is so close to the polar point that it always indicates 
the approximate north pole. Observers in the southern hemi- 
sphere are not so lucky, since there is no bright star placed 
conveniently at the south polar point. 

To anyone observing from the north pole of the Earth's 
surface, Polaris would appear to remain virtually overhead; 
its altitude above the horizon would be greater than 89°. 
At Greenwich (latitude N. 51 \°) the altitude of Polaris is 
51 1°; on the equator (latitude o°) Polaris has of course no 
altitude at all — in other words, it lies right on the horizon. 
South of the terrestrial equator, Polaris never rises, so that it 
will never be seen. 

The point at which the Sun crosses the celestial equator 
in its springtime journey from south to north is known as the 
Vernal Equinox, or First Point of Aries. The Sun reaches 
this point about March 21 each year, and crosses the equator 
once more, this time from north to south, six months later at 
the Autumnal Equinox, or First Point of Libra. The vernal 
equinox is to the sky what the Prime Meridian is to the Earth, 
since all positions are reckoned from it; but we must remember 
that it is a point of definite significance, whereas Greenwich 
was chosen as a standard for longitude merely because the 
famous Observatory happened to have been built there. 

The angular distance of a star eastwards of the Vernal 
Equinox is known as the star's right ascension. It can be given 
in degrees, but is more usually measured in hours, minutes and 
seconds, because such a method is more convenient. 



To explain this, we must refer to the "meridian" of any 
observing point on the Earth, which is the great circle on the 
star-sphere passing through both celestial poles and also through 
the overhead point (the "zenith") of the place of observation. 
Clearly, a star on the "meridian" will be at its maximum height 
above the horizon. The First Point of Aries must pass across the 
meridian at any place once every 24 hours (sidereal time), 
and the difference between this time and the time of the star's 
meridian passage will give us the right ascension of the star. 
For instance, Sirius reaches the meridian 6 hours 43 minutes 
after the First Point of Aries; therefore, the right ascension 
of Sirius in the sky is 6 hours 43 minutes. 

The slight shift of the celestial pole, described in Chapter II, 
means that a star's right ascension and declination alter very 
gradually over the years. In this book (and in most modern 
star atlases) the positions are given for the year 1950, since it 
will be a long time before the error becomes great enough 
to be at all worrying. As a matter of interest, the First Point of 
Aries has shifted so much since olden times that it has moved 
out of Aries altogether, and now lies in the neighbouring 
constellation of Pisces, the Fishes. 

A telescope equipped with setting circles and clock drive 
can be swung to any desired right ascension and declination, 
so that as soon as the position of a body is known the telescope 
can be directed straight towards it, without bothering about 
searching. Since the planets can be found in the same way, this 
is much the easiest method for picking up Mercury or Venus in 
broad daylight. It is clear, of course, that while the right 
ascension and declination of a star will remain virtually con- 
stant, those of the Sun, Moon and planets will alter appreciably 
over a very short period. 

Dividing the stars into constellations, and naming the 
brightest objects, is enough for a rough classification. Most 
of the leading stars have proper names, such as Sirius, Canopus, 
Rigel, Vega and Capella. On the other hand it would be a hope- 
less task to allot special names to each star, and we have 
recourse to letters or numbers. 

A method used by Bayer, who drew up a famous star cata- 
logue in 1603, has stood the test of time so well that it will 
certainly never be altered. On this system, each of the leading 



stars of a constellation is allotted a Greek letter, beginning with 
Alpha for the brightest object and ending with Omega for the 
faintest. In Aries the Ram, for instance, the brightest star is 
Alpha Arietis (Alpha of the Ram), the second brightest Beta 
Arietis, and the third brightest Gamma Arietis. Unfortunately 
the strict order is often not followed, so that the system has 
become rather chaotic. In Orion, Beta is the brightest star, 
followed by Alpha, Gamma, Epsilon, Zeta, and then Kappa, 
with Delta an "also ran". A list of the Greek letters, with their 
English names, is given in Appendix XIX. 

This is all very well, but it can deal only with the 24 principal 
stars in each constellation, which in some cases (such as Orion) 
is not nearly enough. Flamsteed, the first Astronomer Royal, 
preferred to give the stars numbers, beginning in each con- 
stellation with the star of least right ascension. Still fainter 
stars, not listed by Flamsteed, have been allotted numbers 
according to later catalogues, and the result is that each bright 
star has several designations; Rigel in Orion is known also as 
Beta Ononis and as 19 Orionis. As time goes on, the proper 
names of the stars are becoming less and less used, with the 
Greek letters and the numbers taking their places. 

It is also necessary to have some scale of reckoning apparent 
brilliancy. This is done by classification into "magnitudes" 
but the scale sometimes causes confusion, since the lowest 
values indicate the most brilliant objects. Bright stars are of 
magnitude 1, and the faintest visible to normal eyes without a 
telescope are of magnitude 6, while with powerful telescopes 
stars down to the 23rd magnitude can be detected. Modern 
instruments known as "photometers" can measure the bright- 
ness of a star very exactly, and in catalogues the value is given 
to 1 / 100 of a magnitude. Polaris, for instance, is of magnitude 
1 '99, so that it may be regarded as a standard star of the second 

A few stars are actually brighter than magnitude i-o, 
so that they have values of less than unity; examples are Rigel 
(o-o8) and Altair (077), Rigel being appreciably the brighter 
of the two. Four stars— Sirius, Canopus, Alpha Centauri 
and Arcturus — have minus magnitudes. On the stellar 

* The magnitude of Polaris is very slightly variable. 


scale, Venus at its brightest is of magnitude — 4 J, while the Sun 
is about — 27. The magnitude scale is based upon a definite 
mathematical ratio, but this need not concern us at the moment. 
The stars are of different luminosities, and are at different 
distances from us, so that our constellation groups are due to 
mere line of sight effects. In Ursa Major, for instance, one of 
the seven bright stars (Alkaid) is much more remote than the 
other six, while Polaris, in Ursa Minor or the Little Bear, is 
twice as distant as Alkaid. Merely because two stars arc in the 
same constellation, we need not suppose that they have any 




Fig. 49. Diagram to illustrate the principle of parallax. 

connection with each other. There is an easy way of showing 
this. If you look at a gatepost as seen against the background of 
a clump of trees, you do not suppose that the gatepost has any 
real connection with the trees. 

As described by our scale model on page 30, the stars are 
so remote that their distances are not easy to measure. The 
first reliable results were obtained by using the method of 
"parallax", which is interesting enough to be explained more 
fully, even though it is useless for any but the very nearest stars. 

The best way to demonstrate parallax is to make a practical 
experiment with a pencil, holding it up in front of your face 
and looking at it with alternate eyes. First align the pencil with 
some object, such as a vase on the mantelpiece, using your right 
eye only. Now shut your right eye and open your left, keeping 
the pencil still. The pencil will no longer seem to be in line 
with the vase; it will seem to have shifted. If you know the 
distance between your eyes, and the angular amount by which 
the pencil appears to have shifted, you can work out the actual 
distance of the pencil by using fairly simple mathematics (Fig. 
49) . This apparent shift in position is a measure of the pencil's 


si* * 


/ \ 


Much the same principle can be used to measure the distance 
of a relatively near star seen against a background of more 
distant stars, but the base-line used has to be enormously long. 
Fortunately Nature gives us such a base-line ; the Earth swings 
from one side of the Sun to 

the other in a period of six % ^ 

months, shifting 186 million * ^ 

miles in position (Fig. 50) . If 
S is our "near" star, it will ap- 
pear to be at position Si in 
January, but at S2 in July, so 
that if we measure the angu- 
lar shift we can find the dis- 
tance. (The diagram given 
here is hopelessly over-simp- 
lified and out of scale.) The 
actual amount of the shift is 
so minute that it is hard to 
measure, while there are 
numerous corrections to be 
made. However, there is 
nothing complex in the basic 
principle of the method, 
and it was in this way that 
Bessel managed to measure 
the distance of the fifth- 
magnitude star 61 Cygni, in 

The parallax method breaks down altogether for all but 
the closer stars, because the shifts become too small to be 
properly measured. At 160 light-years the method has become 
untrustworthy, and at 600 light-years it is quite useless. In- 
direct methods have had to be developed, and most of these 
involve finding out the actual luminosity of a star as compared 
with the Sun, since as soon as we know the real brilliance and 
the apparent brilliance we can find the distance — much as we 
can judge the distance of a lighthouse if we know the power of 
the lamp and can measure how bright it appears to us. 

Even the nearest of all the stars, Proxima Centauri in the 
southern sky, is immensely remote, so that in comparison even 





Fig. 50. Measuring the distance 
of a star by parallax. El, E2 — 
Earth; S — star; Si, S2 — appar- 
ent positions of S with respect to 
more distant stars. The diagram 
is of course grossly out of scale. 



Fig. 51. The Pointers and the Pole Star. 


Pluto is very close at hand. The distance in miles is about 25 
million million, or 4^ light-years. 

Sirius, which appears the brightest star in the sky, is 26 
times as luminous as the Sun, but it owes its supreme position 
in our skies mainly to the fact that it is relatively close to us, 

since it lies at a distance 
of only 81 light-years. 
Canopus, in the southern 
constellation of Argo 
Navis (the Ship Argo), 
looks only a little less 
bright than Sirius, but is 
a great deal further away, 
so that it is clearly much 
more luminous. It would 
in fact take 80,000 Suns 
to equal Canopus. 

However, we must not 
imagine that our Sun is 
unusually feeble. It may 
be a firefly compared with Canopus, but it is a searchlight 
compared with some of the dimmest members of the stellar 
system. The faint red star known as Wolf 359 has a luminosity 
of only 1 /50,ooo of that of the Sun, so that we need not be too 
humble. If anything, the Sun is rather above the average in 
brilliancy, though there is really no such thing as an "average 

Just as the stars are of different distances and luminosities, so 
they are of different sizes, temperatures and colours. A glance 
at Orion will show that of the two apparently brightest stars, 
one (Betelgeux*) is orange-red, while the other (Bigel) is white 
or slightly bluish. Betelgeux is the larger of the two, but it is 
much the less luminous, and its surface is cooler than that of 
Rigel, In fact, the stars present an almost infinite variety, so 
that it is rare indeed to find two which seem to be exactly alike. 
To the ordinary observer, the stars appear to remain in 
fixed positions. Two of the stars in the Great Bear, Dubhe and 
Merak, always point to the Pole Star (Fig. 51) ; they have done 

♦ This name may be spelled in various ways, such as Betclgeuse and Betelgcuze. 
In using a final x, I have followed the advice of Arabic scholars, 




IV. Tat ansa 

A. Man Imbrium. V. L. Jackson, 1 1 -75-in. reflector, 1958 December 20, aoh. 45m, This is a picture 

thawing a wide area; Plain is the dark- floored crater in the lower part of the Moon. In this and all 

other photographs, south is at the top and west to the Left. 

H. Ptoiemtsus to Walter. G. A. Hole, 24-in. reflector. This shou> two yre:it chain*. Ptolcmjcus- 

Alphansus-Arxachcl and Waltcr-Regionioruanus-l'urbach. The Straight Wall is seen as a bright line 

to the east (right), rather above the centre of the photograph. 

C* East Part of Mare Qrisium. H. Iv. Dnll, is^-in. reflector, 1961 February 10, t6h. This large-scale 

photograph shows fine details on the boundary of the Mare, Pieard, on the Mare, is partly show n to 

the west (left). 

I)- Hysiimis Chit Area. G. A. Hole. 24-in. reflector. The Cleft is well shown, as is the surrounding 

area. The large scale of the photograph shows that the Cleft contains many crater-like enlargements 

along its length. The prominent crater to the south is Triesnecker. 

V. Comparative Lunar Photographs by IS. H. llnlfithl, (/^J in. rtflerlur) 

Upper: Bailly, {Left) 1066 October 6, 05.16. Bailly is well inside the visible disk. (.High/) 190(1 
March 5, 22.59. Here, Bailly is on the terminator, and appears very prominently. 
IsOietr; Marc Humoruni. (Left) 1566 August 9, 03.17. The area is under fairly high light, with 
Gasscndi well shown. {Right) 1966 March 3, 19.58. Here the Marc is close to the terminator, and 
some shadow can be seen inside Gasscndi: the mountainous border of the eastern Mare Hurnoruni 
is seen to advantage. 

VI. Eclipse. Photographs by T. W, Rackham. 6-in, reflector, (lift) Eclipse of the Sun, 1054 
June 30, partial at Cambridge: (a) 1 ih. 20m. (hi 13b. 36m. (c) 13b. 37m. Some clouds can he 
seen in the first view. 

(right) Eclipse of the Moon, January to, 1954, total at Cambridge: (a) oh. 50m. Ih) lb. 32m. 
(c) th. 55m. 

V 1 1 . Dramas* of the Fitmats 
\. Mart, IOOJ March 9, 01.25. ixi in. reflector ■ 460. Patrick Moure. The Syrtis Major is shown 
to the upper left. 

B. Jupiter, 1963 December 7, 16.53, 84 >n. reflector ■ 300. Patrick Moot*. The Rod Spot is shown, 
but the Hollow was not visible. Note that the two Equatorial Belts have merged into a continuous 
dark strip. 

C. Jupiter, n/64 August 23, 03.10. S£ in. reflectors 274. I'aul Doherty, The Equatorial Zone is 
still dark; the Red Spot is shown, with a white spot south and preceding it. 

1). Jupiter, 1966 October 11, 04.14, 10 in, refractor X 330. T. J. C. A. Moseky. The Equatorial 
Belts arc now separate, and the Red Spot is somewhat inclined in its Hollow. 

E, Saturn, 1963 August 7. 00.43. °1 '"• reflector 300. Paul Doherty. The rings arc well shown, 
with the Cassini Division, 

F, Saturn, 1966 August 26, 23.30. SJ in. reflector • 274, Paul Doherty. The rings are almost closed, 
hut the shadow on the disk is prominent. Titan is seen some way front Saturn; the black spot on 
the planet's disk is rhe shadow' of Titan. 


VIII. Photographs of the I'luncts 
isi-in- Cassearain. 1963 November 2, 31 h. 

19111 . 

Long, el cm.: 340 (I) 
10 Pjh. Tin: Rid 

A. Jupiter. II. E 

297 an. 

It. Jupiter. \\. Kippcnjialc, iy(>2 July 30; the best of a series taken from oih 

Spot is beautifully shown. 

C. Jupiter, shotting Transit of Ganymede. W. Kippengale, lyfej September 2S, 23h. 1 0111. 

\>. Jupiter, shotting Sluitlas Transit »j l'i. W. Kippt-nvale, n/>.i Oi-lntiiT j;. jib. iom Conditions 

were misty; the image was steady, but a long exposure needed ([J to 2 sec). 

E. Saturn in 1957: ILK. Dall, 1 5 J-in, CasseKrain. The rings were « idclv displayed ; the main belt 

on ilie disk is shown, as well as the Cassini Division in the rimis. 




X. Comet Hemttil. H170 April 4. I'hotuHrapli by l> r . H. R. Super, Onrluin, Isk- of Man. With its 
loittf tail, it became a prominent nakcd-eyc object. 

XI. Comet ArrnA-Roland, 1957 April 27 
imususil "ftpike" i» well ahown. 

Photograph by Frank J Acfictd, Forest IIjIJ. Tlitr 

XIII. Venus near the Pleiades, F, J, Acfwld, Forest Hall, 11)56 April z. Exposure 10 minutes. 
jr/5.8 camera. 

XIV. Satellite Trail 

This ptotagmph by Howard Miles slums the track of .060 Iota i (Echo i Sudlfte) 
as it passed through the constellation of Orion on March i, „,6 4 ,, j „ SSlffi 

shadow. I he- two brightest star-trails are those of Bctel R eux and IMIntrix 


so for generations, and mil continue to do so for generations 
more. Of course, the old term "fixed stars" is misleading. The 
stars are moving about at high speeds, but they are so remote 
that it takes centuries for bright naked-eye stars to show obvious 
shifts in position, while the tiny annual shifts due to parallax 
can be detected only with the most refined instruments. Over 
the ages, however, the shifts will mount up, and eventually 
the two Pointers will no longer seem to fine up with Polaris. 

The slow movement 
of a star across the 
background is known 
as the star's Proper 
Motion, and must not 
be confused with the 
minute movement due 
to parallax. There is 
also a motion in the 
fine of sight, termed 
Radial Motion (Fig. 
52) . If a star is coming 
straight towards us or 
away from us, it will 
have no proper motion 
at all, and will appear 
to remain still even 
over the lapse of cen- 
turies, but its radial 
motion will be detectable by means of the spectroscope. 

Since the Sun is an ordinary star, the other stars show spectra 
of much the same kind. Temperature differences and other 
factors will cause complications, but usually there will be the 
continuous rainbow crossed by dark absorption lines due to 
gases in the star's reversing layer (page 64). If the star is 
approaching us, the dark lines will be shifted slightly towards 
the violet or short-wave end of the spectrum, while if the star 
is receding the shift will be towards the red. By measuring the 
amount of the shift, we can work out the radial velocity of the 

There is an everyday analogy to this. When a train whistles, 
the whistle is high-pitched so long as the train is coming towards 

L l6l 

Fig. 52, Radial Motion of a star. 

S 1 S2 = actual motion, S 1 A = radial 

motion. AS 2 = proper motion. 


us, because more sound-waves are entering our ears, per 
second, than would be the case were the train standing still. 
After the train has passed by, and begins to draw away, fewer 
sound-waves will reach us per second, so that the pitch of the 
whisde drops. Light can be regarded as a wave-motion, and 
when the source of light is moving away the "pitch" is shifted 
towards the long-wave or red end of the spectrum. This is 
known as the Doppler Effect, in honour of the Austrian physic- 
ist Doppler, who discovered it over a hundred years ago. 

Sweeping the skies with a telescope is a fascinating occupa- 
tion. Some of the stars show vivid colours; some are double, 
and some can be split into three or more components, so close 
together that to the unaided eye they appear as one star. There 
seems to be no end to it all, and no observer can hope to 
examine all the stellar wonders in the course of a lifetime. The 
more lie sees, the more he must realize that our own Solar 
System is a minute speck in space. 


Chapter Thirteen 


Nearly everyone who uses a telescope for the first time 
expects to see a bright star, such as Sirius or Rigel, enlarged to 
a massive globe filling half the field of view. Disappointingly, 
however, nothing of the kind is visible. If the disk of the star is 
of appreciable size, there is something wrong with the telescope 
— since not even the Paloraar 200-inch reflector can show a 
truly measurable disk to any star. 

This is not because the stars are small. Some of them are in 
fact big enough to hold the whole orbit of the Earth. The small 
apparent size is due to the fact that the stars are inconceivably 
remote. No amount of magnification upon our modern tele- 
scopes can improve matters, and if we want to study the stars 
themselves we must resort to indirect methods. 

At first sight, therefore, it would seem as though we could 
never gain much information. But though the telescope is not 
by itself particularly helpful, it can be combined with the 
spectroscope to make a powerful weapon which can be used 
not only to analyse the materials which make up the stars, 
but also to investigate the inner regions, the "power-houses" 
where stellar energy is generated. 

Most stars show spectra which are basically similar to that 
of the Sun (see page 64}, but there are wide variations in detail. 
Over 90 years ago Father Secchi, one of the great pioneers in 
this field, found that there were well-marked "spectral types"; 
for instance, stars like Sirius showed prominent dark absorp- 
tion lines due to hydrogen gas, while in the case of Rigel 
lines due to helium were dominant. Secchi divided the stars 
into four definite groups. A more comprehensive system, 
originated by E. C. Pickering (brother of W. H. Pickering, the 
lunar and planetary observer) increased the number to eleven, 
merging gradually into each other. 

On this latter system, each type is denoted by a letter of the 
alphabet. It was originally intended to take the usual sequence 



of letters, but some of the early classes were found to be un- 
necessary—there is now no recognized Type C, for instance— 
and the series became muddled, until to-day it reads: W, O, B, 
A, F, G, K, M, R, N, S. Some thoughtful astronomer has 
invented the mnemonic "Wow! Oh, Be A Fine Girl, Kiss Me 
Right Now Sweetie", which is at least a good way to remember 
the correct series. 

To describe the features of each type would require many 
pages, but it will be of interest to give a brief outline. The 
series given above denotes an order of decreasing surface 
temperature, W and O stars being the hottest and R, N and S 
the coolest; the Sun, as befits its undistinguished character, 
comes in Type G, somewhere near the middle of the list. A 
refinement is to divide each type into sub-grades, from nought 
to nine, so that A5 is midway between Ao and Fo. 

Some W and O stars, known as Wolf-Rayet stars in honour 
of the two astronomers who first described them in detail, 
have surface temperatures of over 35,000 degrees Centigrade] 
so that they are the hottest of the normal stars. Their spectra 
are peculiar, having in some cases a large proportion of bright 
lines instead of the usual dark ones, and they have set astro- 
nomers many problems, some of which remain to be solved. 
Most Wolf-Rayet stars are very remote, so that they appear 
faint in spite of their great luminosity, though two of them 
(Zeta Puppis and Gamma Velorum) are of the second 
magnitude; Gamma is too far south to rise in England. 

Rigel in Orion has a B-class spectrum, and in fact aU the 
leading stars in Orion are of this type, with the obvious ex- 
ception of Betelgeux. The surface temperatures are in the 
region of 25,000 degrees Centigrade, so that B-stars are highly 
luminous. Somewhat less hot are the A-stars such as Sirius, 
with temperatures of about 1 1,000 degrees Centigrade; stars of 
type F, such as Canopus, are cooler still. Procyon is also of 
type F. Hydrogen and helium lines are less conspicuous, but 
calcium vapour is much in evidence. 

The Sun is a typical G-type star, with a surface temperature 
of 6,000 degrees Centigrade. Here, of course, our investigations 
are helped by the fact that the solar spectrum can be studied in 
great detail. Another good example of a G-star is Capella, 
which appears as one of the most conspicuous stars in our skies. 



The remaining types are orange (K) or orange-red (M, 
R, N and S), with temperatures ranging from 4,200 degrees 
down to only 2,000 degrees. Types N, R and S are compara- 
tively rare, and most of them are variable in brightness, while 
their spectra are complex and not at all easy to interpret. 
Arcturus in Bootes is of Type K, while Betelgeux, Mira in 
Cetus, and Antares in Scorpio belong to Type M. 

It may be convenient to group the stars in this way, but we 
have only touched the fringe of the problem. Consider, for 
instance, two M-type stars, the brilliant Betelgeux and the dim 
Wolf 359. Betelgeux shines as brightly as 15,000 Suns, while 
Wolf 359 is a feeble body with only 1/50,000 of the Sun's 
candle-power, so have we any reason to class them together 
in the spectrum sequence? To say the least of it, they are ill- 
assorted companions. 

One of the great discoveries of the early twentieth century 
was that apart from types W, O, B and A, the spectral classes 
tend to be separated into "giants" and "dwarfs". We can find 
many M-giants like Betelgeux, and many M-dwarfs like Wolf 
359, but M-stars of intermediate luminosity are virtually absent. 
When it became possible to estimate the diameters of the stars, 
the distinction between giants and dwarfs became even more 
evident. Betelgeux is a vast globe about 200 million miles 
across, whereas Wolf 359 has a diameter of less than a million 
miles. If we picture a scale model and make Betelgeux a globe 
with a diameter equal to that of a cricket pitch, Wolf 359 will be 
represented by a croquet ball. 

The discovery of the giant and dwarf divisions was followed 
by a very simple, straightforward theory about the life-history 
of a star. It was assumed that in its early life, soon after it 
condensed out of the interstellar dust and gas, a star was hardly 
hot enough to emit visible light. Naturally, it would tend to 
shrink, because the force of gravity would tend to pull all its 
matter together; this would cause heat, so that the star would 
become a large Red Giant like Betelgeux. As the shrinking went 
on, the star would become an Orange Giant (type K) and 
then a Yellow Giant (type F), before turning into a smaller but 
very hot Wolf-Rayet or B star. As would be expected on this 
theory, the most luminous white types are not divided into 
giants and dwarfs. 

i fi 5 


This would be the peak of a star's career. It would go on 
shrinking, but it would also become cooler, since its main 
energy would have been spent. It would pass down the dwarf 
series or "Main Sequence", becoming first an F-dwarf, then a 
G-dwarf like the Sun, and then a small, red star of one of the 
later types, finally losing all its heat and changing from a dim 
red dwarf like Wolf 359 into a cold, dead globe. 

It all sounded beautifully simple. Unfortunately, serious 
complications have become evident, and it is now certain that 
the true life-history of a star is much more complicated than 
this. It seems definite, for instance, that the "power-house" deep 
inside the globe is a true power-house, and that the radiating 
energy of a star is not due solely to the heat set up by shrinking. 
The source of stellar energy is the rearrangement of the atoms 
which make up the body of the star. 

What happens in the case of an ordinary main sequence star 
like the Sun is that nuclei of hydrogen atoms, which are far more 
plentiful than all the other types of atoms put together, build 
up into nuclei of another gas, helium. It takes four hydrogen 
nuclei to build one helium nucleus, and each time the combina- 
tion occurs a certain amount of energy is let loose. It is this 
released energy which keeps the star radiating. 

Of course, the whole process is extremely complex, and to 
enter fully into the mechanism would be beyond my present 
scope. But one thing is clear: the supply of hydrogen "fuel" 
cannot last indefinitely. When it begins to run low, the star 
must rearrange itself drastically. The interior shrinks, while the 
outer layers expand and cool; the star becomes a Red Giant. 
Heavier elements are built up from the helium, and the temper- 
ature at the core rises to fantastic values. The star may become 
unstable. If it is very massive, it may explode as a supernova. A 
more modest star, such as the Sun, will avoid such a fate, but in 
any case it must eventually use up all its nuclear reserves. After 
its period of glory as a Red Giant, it will presumably collapse, 
rather abruptly on the cosmical time-scale, into a small and 
incredibly dense star of the type known as a White Dwarf. 

White Dwarfs are among the most curious objects in the 
entire sky. They are certainly plentiful, but they are so faint 
that they are not easy to detect unless they are relatively close 
to us. Yet they are not unusually cool; some of them have 



peculiar spectra, indicating a surface temperature as great as 

that of Sirius, and much greater than that of the Sun. Their 

faintness must therefore mean that they are very small. One 

extreme example, Kuiper's Star, has a mass equal to the Sun 

but a diameter of only 4,000 miles, no more than that of Mars. 

The mass of the Sun, but the diameter of Mars! There 

is only one way in which so much matter can be packed into so 

small a globe : the matter must be extremely dense. If a man 

could be taken to the surface of Kuiper's Star, he would find 

that he had a weight of 250,000 tons judged by our standards, 

while a thimbleful of the material of die star itself would weigh 

several thousandsof millions of tons if it could be measured on the 

surface of the White Dwarf. Matter in such a state is completely 

beyond our understanding; we cannot conceive how it would 

be possible to pack so many tons weight into a thimble, and this 

amazing density has far-reaching results. For instance, the whole 

atmosphere of Kuiper's Star is probably less than twenty feet deep. 

It seems very likely that a star such as the Sun will end its 

career as a White Dwarf. Yet a very massive star will behave in 

a much more spectacular fashion. It will explode as a supernova, 

and the actual remnant of the old star will be a very small, 

rapidly-spinning object made up of neutrons. Many of these 

neutron stars have now been detected by their long-wave radio 

emissions, though only two {one in the Crab Nebula, the 

other in Vela) have been optically identified. Because of 

their rapidly-varying radio emissions, these objects are called 


Suppose that we have a star whose initial mass is greater 
still? When the nuclear reserves are used up, collapse will 
begin; but instead of a supernova outburst, there will be a 
quicker and quicker collapse to a remarkably small size and 
incredible density. Eventually, not even light will be able to 
escape, and we are left with what astronomers call a "black 

Obviously, black holes cannot be seen directly, but we suspect 
the locations of a few. In Auriga (Map IV, page 272) there 
is a strange star, Epsilon Aurigae, once thought to be made up 
of two components: one giant, and one very large, cool star 
with a diameter of about 1 800 million miles. It has now been 
suggested that the cool secondary may not be a star of normal 



type, but a black hole. Whether this is true or not remains to be 
seen, but it is at any rate a possibility. 

In any case, even normal stars are very unequal in size, 
density and luminosity, but not nearly so unequal in mass, as 
the large bodies are rarefied and the small ones dense. Few stars 
are known with ioo times the mass of the Sun, while the light- 
weights of the stellar system, the twins which make up the double 
star L726-8, still have ^ of the solar mass, and are thus far more 
massive than Jupiter. Nature can play some strange tricks. 

o SUN 

Fig- 53- Section of Epsilon Auriga (larger component) 
showing size compared with that of the Sun. 

This shows, too, that there is a major difference between a 
small star and a large planet. Though Kuiper's Star is only the 
size of Mars, it is completely non-planetary in nature. Not only 
is it luminous, but it is fax more massive than any planet could 
possibly be. 

Planets moving round other stars are too faint to be observed 
directly, but are probably abundant. The first to be detected 
moves round our old friend 61 Cygni {or, more accurately, round 
one of the components of the 6 1 Cygni system) ; it seems to have 
a mass 15 times that of Jupiter, and was tracked down because 
it exerts a pull upon the visible star, affecting the star's proper 
motion. Another case is nearby red dwarf, Barnard's Star. In 
1963 P. van de Kamp was able to announce that Barnard's Star 
is associated with a body only 2§ times as massive as Jupiter, and 
which must almost certainly be a planet. It may even be that 
there are two planetary attendants, each of rather lower mass. 

It is impossible to do more than mention a few of the other 
curious bodies to be met with in the stellar heavens. Some stars 
seem to be surrounded by immensely distended atmospheres, 
while others, such as the remarkable object 48 Librae, are "shell 
stars" with double atmospheres, the outer shell giving an impres- 
sion of a flattened ring which puts one in mind of the ring-system 



of Saturn, though there is of course no real analogy. A few 
of the feebler Red Dwarfs appear to be subject to violent 
flares, so that they can increase perceptibly in brilliance and 
then fade back to normal over a period of only a few minutes. 
Then, too, there are the "supergiants" such as Canopus in 
Carina and Deneb in Cygnus, celestial searchlights with spectra 
that distinguish them at once from their milder fellows. 

Recently much has been heard about "radio sources", which 
emit long-wave radiation and are studied by means of special ap- 
paratus. Oddly enough, these objects are not ordinary stars at all. 

A radio telescope collects radio waves in roughly the same 
manner as an optical telescope collects light-waves ; no actual 
picture of the course is produced, but the information gathered 
is remarkably valuable, and radio astronomy has become one of 
the most vital branches of modern astronomical science — even 
though it began only in the 1930s (see Appendix XXIX). Most 
people are familiar with the appearance of the great 250-foot 
"dish" at Jodrell Bank, but it is worth pointing out here that not 
all radio telescopes are built upon the dish pattern. Different 
investigations need different techniques and instruments. 

Radio sources are of various kinds. The Sun, of course, is a 
powerful emitter of radio waves, and radiations have also been 
recorded from Jupiter (though, as we have seen, their exact 
nature is still uncertain). In our Galaxy, we have various 
objects such as the Crab Nebula in Taurus, which will be 
described below, and which is the wreck of a supernova — a 
star which suffered a cataclysmic outburst long ago. The Crab 
is about 6,000 light-years away; it contains one of the objects 
known as pulsars, which are rapidly-vibrating radio sources, 
and which are quite definitely neutron stars, far denser and 
smaller even than the White Dwarfs. It is now known that a 
pulsar represents the very last stage in the active career of a 
very massive star. 

This book deals with optical astronomy; I am not a radio 
astronomer, and am not therefore competent to act as a guide to 
others, but it is worth noting that even in this technical field 
there is scope for amateur research. The possibilities are almost 
unlimited; and by learning something about what is going on 
in the depths of space, we shall also form a better appreciation 
of the nature of the universe itself. 


Chapter Fourteen 


Of all the the constellations in the sky, probably the best 
known is the Great Bear. It is not so brilliant as Orion, nor 
so spectacular as the Southern Cross; but it can always be seen 
in England when the night sky is clear, and most people have 
developed an affection for it. Besides, it is useful because two 
ofits seven chief stars point to the Pole. 

Even a casual glance will show something interesting about 
the "second star in the tail", known as Mizar or, on Bayer's 
system, Zeta Ursae Majoris. Mizar itself is of the second magni- 
tude, but close beside it is a much fainter star, Alcor, so dim 
that it is not particularly easy to see when there is the slightest 

Double stars of this kind are extremely common in the 
heavens, though most of them are too close together to be 
separated without the help of a telescope. They are spectacular 
enough to be well worth looking at for pure enjoyment, particu- 
larly when the two components are of different colours, and they 
are also useful for testing the performance of a telescope. A 
list of suitable "test pairs" is given in Appendix XXIII. 

There are two classes of double stars. Sometimes the two 
members of a pair are not physically connected, so that the 
effect is due merely to the fact that one star happens to lie 
almost behind the other. One way to explain this is to picture 
two motor-cyclists coming down a long stretch of darkened 
road, using their headlamps and separated by perhaps half a 
mile. An observer watching them approach may well imagine 
that they are riding side by side, particularly if the nearer 
cyclist has the less powerful lamp. However, "optical" double 
stars of this type are not so common as might be imagined. 

The physical connection between the components of some 
doubles was first realized a century and a half ago by Sir 
William Herschel. Actually, Herschel made the discovery more 
or less by chance. He was trying to measure the distances of 
some of the stars by the parallax method (see page 159), and 




he had made long series of observations of pairs which he 
thought might show an annual shift. He failed in his main 
object, because his instruments were not sufficiently accurate; 
but he did find that many of the doubles formed physically 
connected systems, and were in orbital motion round each 
other. Nowadays these genuine pairs are known as "binary 

It is not correct to say 
that the less massive star 
of a binary system re- 
volves round its senior 
companion. Though the 
two may be very unequal 
in size and brilliance, 
they will certainly not 
be violently unequal in 
mass, since — as we have 
seen — the stars are 
strangely uniform in this 
respect; indeed, the 
smaller component may 
well be the more massive 
of the two. What will 
happen is that the two 
bodies will move round 
their common centre of 
gravity, much as the two 
bells of a dumb-bell move 
when twisted by their 
jointing arm. 



Figs. 54 and 55. In Fig 54 the 
bells are equal in mass, and the 
balancing point B is midway be- 
tween them; in Fig. 55 the bells 
are unequal in mass, and B is no 
longer at the mid-point of the 
joining bar. 

If the two components have equal mass, the centre of gravity 
will he half-way between them, just as we can balance the 
dumb-bells by the middle of the arm (Fig. 54). If one star is the 
more massive, the centre of gravity will be displaced towards it 
(Fig. 55). The Earth and Moon move in this way; but since 
the Moon is so much the less massive, the centre of gravity of 
the system lies some way inside the Earth's globe. 

A pair of binoculars will show that many apparently single 
stars consist of two, and a small telescope will reveal hundreds of 
pairs. Sometimes the components are equal, so that they are 



_ Quine twins, but more often one star is much brighter than 
the other. If a brilliant body is concerned, it may tend to drown 
its companion in a blaze of light, so that a telescope of some 
size will be needed to show both objects. Sirius is an excellent 
example of this. The brighter component is the most brilliant 
star in our skies, and it overpowers the White Dwarf companion, 
even though the White Dwarf would be an easy telescopic 
object were it shining on its own. 

Binary stars have proved to be most useful to the theoretical 
astronomer. The orbits can be worked out; and as soon as the 
distance and the period of revolution are known, the combined 
mass of the stars in the system can be derived. Suppose, for 
instance, that the stars in a pair lie at an average distance from 
each other of 93 million miles, and have a period of one year. 
The Earth revolves round the Sun at this distance and in this 
time, and this means that the combined mass of the Sun-Earth 
pair must be equal to the combined mass of the two stars in 
the binary. In practice, we can neglect the Earth, which is of 
negligible mass when compared with any star, and in the above 
instance the two components of the binary would together 
equal one body the mass of the Sun. Unfortunately, calculating 
the separate masses of the components is not so straight- 

The whole method depends upon careful measurements of the 
apparent relative motions of the twin stars, and it is therefore 
not surprising that most of the bright pairs have been so closely 
studied by professional astronomers that there is not much 
point in the amateur's observing them further. Yet some of the 
generally-accepted measures are out of date, and there is 
definite scope for the serious observer with adequate equipment. 

The separation of a double star is measured in seconds of 
arc. When it is borne in mind that the apparent diameter 
of the Moon is about half a degree, or 1,800 seconds of arc, it 
is evident that a pair of stars with a separation of only a second 
or two will need a powerful telescope if it is to be split. The 
apparent distance between Mizar and Alcor is roughly 700 
seconds, but when a telescope is used the bright star is itself 
seen to be double, made up of two components between 14 
and 15 seconds of arc apart. Actually, tile system is more 
complicated even than tins. 



There is a minor mystery connected with Alcor. The old 
Arab astronomers called it "a test for keen eyes", but nowadays 
it can be seen by any normal person when the sky is clear 
and it can in no sense be regarded as a test. Either Alcor has 
brightened up during the last thousand years, or else it k not 
the star referred to by the Arabs. The real test star may be 
the much fainter object lying between Mizar and Alcor. This 
star is usually below the 8th magnitude, and thus quite in- 
visible without a telescope, but it has been suspected of 

The "position angle" of 
a double star, binary or 
otherwise, is the direction of 
the fainter star as reckoned 
from the brighter, begi nnin g 
with o degrees at the north 
point and reckoning round 
by east {90 degrees), south 
(180), and west (270) back 
to o, as shown in Fig. 56. 
This is generally enough to 
enable one to form a mental 
picture of the double before 
one actually goes to a tele- 
scope, though in the case of 

perfect twins it is not easy to tell which of the components is 
meant to be the senior partner. 

Measuring the separations and position angles of double 
stars cannot be undertaken with a telescope of less than 6 inches 
in aperture, and it is also necessary to have an equatorial 
mount, a driving clock, and a measuring device known as a 
micrometer. Micrometers are of various types; to describe them 
here would be beyond our scope, but full information can be 
found in the works listed in Appendix XXXII. 

The most beautiful of the double stars are those which show 
contrasting colours. Pride of place must go to Albireo or Beta 
Cygni, the faintest star in the "cross" of Cygnus, the Swan (Map 
VIII) . The main star is of the third magnitude, and is of a strong 
golden-yellow colour, while the fifth-magnitude companion is a 
glorious blue-green, The two are sufficiently wide apart to be 


Position angle. 


well seen in a 2-inch telescope, and a power of 50 on a 3-inch 
refractor will show them excellently. Other yellow and green 
pairs are known, but in my opinion, at least, none can rival 

There are also cases of bright orange-red stars, usually of 
Type M, which are accompanied by small green companions, 
Antares, leader of the Zodiacal constellation of Scorpio, is one 
of the reddest of the brilliant stars — its very name means "Rival 
of Mars"— and has also the distinction of being one of the 
largest giants known, so that in itself it is remarkable. Its 
beauty is enhanced by the fact that a small telescope will 
reveal an emerald-green star close beside it. The greenness 
of the faint companion is due partly to contrast with the 
ruddy hue of the giant, but it is none the less spectacular for 

Now and then we meet 
with some oddly-assorted 
pairs. One of the most 
interesting is Sirius, the 
Dog-Star (Map V). The 
main component is an A- 
type giant with a lumin- 
osity 26 times as great as 
the Sun's, and a diameter 
of more than a million 
miles. The second star 
could hardly be more 
dissimilar; it is a 
White Dwarf, consider- 
ably smaller than Uranus, but with a mass almost equal to 
that of the Sun. In Fig. 57, the sizes of the two companions are 
shown, with the Sun added for comparison. 

Since Sirius has always been known as the Dog-Star, the 
White Dwarf companion has acquired the nickname of "die 
Pup", but at least it is a pup which can make its presence felt, 
like Neptune, it was tracked down by its gravitational pull 
long before it was actually seen. Bessel, famous as the first 
astronomer to measure the distance of a star, found that Sirius 
itself was wobbling slightly in the heavens, and he calculated 
that this must be due to the effect of an unseen companion. 


Fig. 57. Comparative sizes of Sirius 
A, Sirius B and the Sun. 


Years later, in 1862, the Pup was discovered, quite by chance, 
by an American instrument-maker who was testing a large new 

Though the two stars of the Sirius pair are so unequal in 
size and luminosity, the bright giant has a mass only 2| times 
as great as that of the White Dwarf. The distance between the 
two is about equal to that between Uranus and the Sun, and the 
period is about fifty years, so that two complete revolutions have 
been completed since the Pup was first seen. As a matter of 
fact, the Pup does not appear to be particularly faint, but 
it is not easy to observe, since the glare from the larger star 
drowns it. It has been claimed that a 6-inch telescope will 
show it, but I admit that I have yet to see it with my 
i2£-inch reflector, probably because Sirius lies well south of 
the celestial equator and so never rises high above the horizon 
in England. I have, however, seen it with the 24-inch reflector 
made and used by G. A. Hole in Sussex. 

Some double stars are 
too close to be split with 
any telescope, but can 
nevertheless be detected 
by means of our old and 
reliable ally, the Doppler 
Effect. In the very much 
over-simplified diagram 
given in Fig. 58, it is as- 
sumed that the fainter star 
(B) is revolving round 
the brighter (A). In posi- 
tion 1, B is moving 
towards us, and its spec- 
trum will show a violet 

shift; in position 2, it will be receding, and the shift will be 
towards the red. Consequently, the combined spectrum due 
to the two stars will show variations, and the binary nature of 
the system will be betrayed. Even if the spectrum of one 
component is too faint to be seen at all, the wobbling of the 
lines of the other star will be just as tell-tale. Pairs of this kind 
are termed "spectroscopic binaries". 

Now and then we meet with positive family parties of stars, 


Fig. 58. The Doppler Effect for 
spectroscopic binaries. 


systems including three, four or even six components. One of the 
best known is Epsilon Lyrae, shown in Map VIII, lying close to 
the brilliant star Vega, which appears almost directly overhead 
in England during summer evenings. Keen eyes can see that Ep- 
silon is made up of two components, and in binoculars the pair 
can be well seen, since the apparent distance between them is 
207 seconds of arc, A 3-inch telescope reveals that each com- 
ponent is again double, so that there are four visible stars in the 
system (Fig. 59), and to make things even more complex one of 
the four is itself a spectroscopic binary. The two main pairs are 
so far apart that they take at least a million years to complete 
one revolution around their centre of gravity. 

Equally remarkable is Castor, 
one of the main stars in the 
famous constellation of Gemini, 
the Twins (Map V). Here we 
have two bright components at 
present 1 -8 seconds of arc apart, 
though the revolution period is 
380 years and it is not nowso easy 
to split the pair as it used to be half 
a century ago. Each is a spectro- 
scopic binary, and there is a 9th- 
magnitude spectroscopic binary 
companion 73 seconds of arc 
away, so that the system of Castor 
is made up of six separate suns. 
On the other hand, Gamma Virginis, in the Y of Virgo 
(Map VI) is at present a grand, easy double separable in a 
very small telescope. By the end of the century it will have 
closed up so much that it will appear single in ordinary 

The magnification for looking at any particular double star 
must depend upon the individual double itself. If you want to 
obtain an overall view of Mizar and its companions, a low 
power is necessary, since if you increase the magnification you 
will find that Alcor is out of the field. Closer pairs naturally 
need higher powers, and for measuring work considerable 
magnification must be used. 
Useful research can be carried out by the amateur double- 


Fig. 59. The famous 

"double-double" star 

Epsilon Lyra. 


star observer ; there is still routine work to be done, and in any 
case there is much enjoyment to be gained from looking at the 
pairs and groups of suns. With their varied separations and 
their lovely contrasting colours, they are among the most 
beautiful of the objects in the stellar heavens. 




Chapter Fifteen 


Fortunately for us, our Sun is a steady, well-behaved 
star. It may have periods of unusual activity, when its disk 
is disturbed by spot-groups and flares, but at least its output of 
energy does not alter greatly over the lapse of hundreds of 

Other suns arc not so quiescent. Some of them vary in bright- 
ness from day to day, even from hour to hour, either regularly 
or in an erratic manner. They swell and shrink, and their 
temperatures change with their fluctuations, so that any planet 
circling round them would be subject to most uncomfortable 
changes of climate. 

Variable stars are important both to the professional and to 
the amateur, and the owner of a small instrument can do 
useful work, particularly as his telescope need not be so perfect 
as that of the lunar or planetary observer (though, of course, 
the better the telescope the better the results). It is true that the 
regular variables of short period have been closely studied at the 
great observatories, but there are other stars which seem to 
delight in springing surprises, so that they need constant 

It is not easy to give a general classification of the different 
types of variable stars. However, the following rough notes 
may be useful as a guide. 

First there are the eclipsing binaries, such as Algol in 
Perseus, which are not true "variables" at all, even though they 
do seem to alter in brightness. Perhaps the most important 
of the true short-period variables are the Cepheids, so named 
because the star Delta Cephei is the best-known member of the 
class ; the periods range from a few days up to six or seven weeks. 
Of much shorter period are the RR Lyree stars, whose periods 
range between 30 hours and less than 2 hours. Then there are 
the long-period variables, usually Red Giants of great size and 
comparatively low temperature, with periods ranging from 70 
days to over 2 years. Irregular variables, as their name suggests, 


behave in an unpredictable manner. Lastly come the violently 
explosive "temporary stars" or nov^. 

There are several variables which can be followed without 
any telescope at all. The most famous of these is Betelgeux, the 
Red Giant in Orion, It belongs to the irregular class, though 
there is a very rough period of from 4 to 5 years, and it changes 
in brightness from magnitude o down to 1,* so that whereas it 
may sometimes almost equal the glittering Rigel it may at 
others be comparable with Aldebaran, the "Eye of the Bull". 
The alterations are slow, but they become noticeable over a 
week or two, and the beginner who estimates the magnitude 
of Betelgeux every few days will soon be able to detect the 
fluctuations. However, most of the interesting variables cannot 
be followed without a telescope or at least binoculars, since 
when near minimum they are below naked-eye visibility. 

Before coming to the proper variables, it will be of interest 
to say something about the "fake variables", or eclipsing 
binaries. These might well have been described in the chapter 
dealing with double stars, but since they do seem to change in 
brilliancy they come under the scope of the variable star 

The best-known of these "fakes" is Algol, which lies in the 
constellation of Perseus and is shown in Map VII. In mythology, 
Perseus was the hero who slew the fearful Gorgon, Medusa, 
whose glance turned the hardiest onlooker to stone, j 1 and it is 
fitting that Algol should mark the Gorgon's severed head. 

Usually Algol shines as a star of magnitude 2*1, only a little 
inferior to Polaris. It remains constant (or virtually so) for a 
period of 2 J days, but then it starts to fade, until after about 
five hours it has dropped to magnitude 3-3. After a relatively 
brief minimum, it starts to brighten once more, taking a 
further five hours to regain its lost lustre. Textbooks usually say 
that its variations were discovered by Montanari in 1667, but 
the old Arab astronomers called Algol "The Winking Demon", 
which is interesting if they were unaware of its odd 
behaviour— as they seem to have been. 

* In a recent catalogue of variable stars, that of Kukarkin, the greatest brilliancy 
of Betelgeux is given as magnitude 0-4; but past records seem to show that on 
rare occasions the star can attain magnitude o*i or even o-o, brighter than any 
other stars in the sky except Sirius, Canopus, Alpha Centaur! and A returns. 

t Nowadays, this power is possessed only by the Chancellor of the Exchequer, 



Algol is not truly variable. The apparent fluctuations are 
due to the fact that the system is a binary, and when the brighter 
star is eclipsed by the fainter the total brightness naturally 
drops. When the fainter star is obscured by the brighter, there 
is a small minimum, but since this amounts to only one- 
twentieth of a magnitude it cannot be detected with the naked 
eye. Actually the system of Algol includes a third star, but the 
principle of the variations is straightforward enough. 

The beginner may like to plot Algol's "light-curve". A 
light-curve is merely a graph plotting time against magnitude, 
as shown in Fig. 6b, and it is always interesting to make one 
from personal observations. In the diagram of Algol given 
here, the secondary minimum is slightly exaggerated, as other- 
wise it would not be visible upon a chart drawn to so small a 

Another bright eclipsing binary is Beta Lyne, which lies 
near the brilliant Vega {Map VIII). Here there are two bright 
components, so close together that they almost touch, and in 
consequence too close to be seen separately in any telescope. At 
maximum, when both stars are shining together, Beta Lyne 
appears of magnitude 3 -4. It then fades steadily to magnitude 
3 -8, and then rises once more to 3 -4, but at the next minimum 
it descends to 4-4, so that deep and shallow minima take place 
alternately. The brightness is always varying, so that there is 
no long comparatively steady maximum, as with Algol. One 
remarkable fact about the components of Beta Lyrae is that 
each is stretched out into the shape of an egg, simply because the 
two stars are pulling so strongly on each other; the general 
situation has been compared to two eggs rolling about with 
their sharper ends kept close together, 

Epsilon Aurigae is also an eclipsing binary (Map IV), though 
its nature is still problematical. The period is over 27 years, 
the longest known for any eclipsing star. Its neighbour in the 
sky, Zeta Aurigae, has a period of 972 days, and is particularly 
interesting to spectroscopic workers because the smaller star 
shines for some time through the outer layers of the diffuse 
giant component before disappearing behind. The fluctuations 
of Epsilon and Zeta Aurigae are however much less obvious 
than those of Algol, and are not marked enough to be noticeable 
with the naked eye, 




^ f 

= 3 " 

— ■ s 












30 SO 70 

CUija 2 A 


: : : ::::i. ~: : x ___ 

8 -A- 

. _ _ _ql ^ 4 _ _ 

t \ 

* - J-. 

N H _L ±il!«M_ 4 

— 1 - ■ 

\ Z_L _ N 3L X 

12 - v~ - 

. \ ./± _ X /_ 


. \ J -X - %* ^ — 

■^■■Li^l 1 1 1 1 1 

1971 Mar Jm Sep 

1972 Mar Jul Sep 1973 Mar Jin Sep 


' ■ 





















6 J 5 « : 



t E ~ y z 

' 1970 


":: ^+ j: 



B70 1971 

Fig. 6o. Light-curves of variable stars. 
(i) Algol: eclipsing binary. 
{2) Delta Cephei: prototype Cepheid. 

(3) R Cygni: Mira type. From my observations of 197 1-3 : 12 J in. 

(4) R Coronae, 1972: a typical minimum. Between August 1972 
and October 1973 the magnitude remained almost constant 
at 6. 12^ in. reflector. 

(5) SS Gygni, 1970: again I used my 12J in. reflector. Four 
maxima occurred. 

(6) HR Delphini, 1967-73: binoculars till 1969, then my 12 J in. 
reflector. The slowest nova on record! 



Turning now to genuine variables, we must begin with the 
Cepheids, which are of great importance because they are 
obliging enough to act as "standard candles". Several are 
visible without a telescope, the best known being of course 
Delta Cephei itself, which lies fairly close to the north celestial 
pole (Map VII) and therefore remains permanently above the 
horizon in England. The period is 5J days, with a magnitude 
range of from 3 -5 to 4-4, and the light-curve is not symmetrical ; 
the rise from minimum to maximum is quicker than the 
subsequent fall, and this is always the case, since Delta Cephei's 
variations are so regular that the period is known to within a 
fraction of a second. 

A Cepheid seems to be a pulsating star, expanding and 
contracting rather in the way that a balloon will do if air is 
forced in and out of it. This is no mere theory ; it has been 
proved, not by the telescope but by the Doppler Effect. When 
a Cepheid is expanding, its bright surface is moving towards 
us, and the lines in the spectrum are shifted towards the violet; 
when the star is contracting, the surface is receding from us, 
and the shift is towards the red. In general, Cepheids have a 
small magnitude-range (the Pole Star is actually a Cepheid, 
though its fluctuations are too slight to be detectable with the 
naked eye) and spectroscopic studies of them are of great 

Equally important is the Period-Luminosity Law, which 
has provided the stellar astronomer with one of his most 
powerful weapons. Reduced to its simplest terms, this Law links 
the variation period of a Cepheid with the star's actual 
luminosity, so that variables of equal period have the same 
candle-power. Delta Cephei, period 5J days, is approximately 
660 times as luminous as the Sun; therefore, every Cepheid 
with a period of 5! days is 660 times as luminous as the 

This by itself would be intriguing enough, but it has far- 
reaching consequences. If we know the real brightness of a 
distant lighthouse, and we can measure how bright it appears 
to be, we can work out its distance from us by means of simple 
arithmetic. In the case of Delta Cephei, we know its real 
luminosity and its apparent magnitude, so that its distance 
follows at once ; it proves to be 1 300 light-years. In fact, we can 



find out the distance of any Cepheid merely by watching how 
long it takes to vary from maximum to maximum. 

The Law has been known now for seventy years and there 
is no doubt of its validity. The longer the period, the more 
luminous the star. These strange variables are the stand- 
ard candles of the universe, and they never depart from their 
own rules, even though we know them to be less uniform in 
type than used to be believed. 

Consequently, we find that we have the means of measuring 
the distance of a remote star-cluster or galaxy. If we can detect 
a Cepheid, we can find its distance, and so the distance of the 
cluster which contains it must be the same. Nature can be 
awkward at times, as we know to our cost, but in this case she 
has given us an unexpectedly accurate measuring-rod. There 
are certain complications, since there are two different types 
of Cepheids with rather different period-luminosity rela- 
tionships, but refinements of this nature do not seriously 
mar our space-gauging. 

RR Lyne stars were formerly classed with the Cepheids, 
but it now appears that they form a separate group. Their 
fluctuations are perfectly regular, and their periods range from 
only 1 1 hours up to slightly more than a day. All RR Lyrae 
stars have about the same' luminosity, roughly 85 times that of 
the Sun, so that they too can be used as standard candles. All 
are distant, and so appear too faint to be easily studied by the 
amateur observer. 

The periods of the eclipsing binaries, the Cepheids and the 
RR Lyra? stars, are known so accurately that there is no point 
in the amateur's observing them further. Nor do any reasonably 
bright variables of such types remain to be discovered. On the 
other hand, the long-period stars present very different 
problems. They are not perfectly regular, and they are not so 
closely studied by professional astronomers, so that here the 
amateur can come into his own. 

In August 1596, David Fabricius recorded a third-magnitude 
star in the constellation of Cetus the Whale, not far from Orion 
(Map IV). By October it had disappeared. Bayer saw it again 
in 1603, when he was drawing up his star catalogue, and gave it 
the Greek letter Omicron, but shortly afterwards it vanished 
once more. Not until some time later was it found that the star 



appears with fair regularity; it takes approximately 331 days to 
pass from maximum to maximum, and it is visible to the naked 
eye for many weeks at a time. Not unnaturally, it was given the 
name of Mira, "The Wonderful". 

The period of naked-eye visibility is not always the same, 
and nor is the magnitude at maximum. At some maxima, as in 
1969, the star attains the 2nd magnitude, and remains visible 
without a telescope for over 20 weeks, but in other years it be- 
comes no brighter than magnitude 5. In 1868, for instance, it was 
a naked-eye object for only 12 weeks. Near minimum the magni- 
tude falls to below 9, so that Mira cannot then be found even 
with binoculars or a small telescope. Nor is the period constant; 
the 331 days given in most textbooks is merely an average, and 
may fluctuate to the extent of more than a month either way. 
There is nothing neat or precise about "the Wonderful Star", 
and for this reason alone it is worth keeping under watch. Extra 
interest is added by the tiny white companion, so faint that it is 
hard to see except when the senior star is near minimum. 

like all long-period variables, Mira is a Red Giant, large, 
cool and diffuse. Many similar stars are known, some of which 
can be seen with the naked eye when at their brightest, and our 
knowledge of their behaviour depends mainly upon the results 
of amateur work. There is no period-luminosity law, and thus 
the stars cannot be used as standard beacons, with the result 
that professional astronomers do not study them so closely as in 
the case of the Cepheids. Again there is a pulsation as well as a 
change in temperature, but the whole behaviour of the stars 
is different. It is rather strange to find that stars with 
the longer periods often prove to be of relatively low lumi- 

Though the long-period stars are at least pardy regular, 
there are some variables which seem to be completely erratic. 
These irregular variables are perhaps the most fascinating of 
all, since one never knows what they are going to do next. 
Betelgeux is one example, and other Red Giants which behave 
in a similar way are Alpha Herculis (Map IX) and Mu Cephei 
(Map VII). Mu Cephei is particularly interesting. It varies 
between magnitudes 3-6 and 5-1, so that it can always be seen 
with the naked eye, but a pair of binoculars will show that it is 
of a beautiful red colour. It looks almost like a drop of blood, 



and it deserves the name of "the Garnet Star" given to it by 
Sir William Herschel. 

Cassiopeia, the Queen, is one of the most prominent of the 
northern constellations, and few people can mistake its five 
chief stars, which are arranged in the form of a rough W (Map 
VII). The middle star of the W, Gamma Cassiopeia, is an 
interesting variable. It used to be ranked as a steady body of 
magnitude 2-3, but in 1936 it abruptly brightened up by over 
half a magnitude, so that it far outshone Polaris. Since then it 
has varied between magnitudes 2 and 3-3. Its spectrum is so 
peculiar that it cannot be placed in any ordinary type. 

Telescopic irregular variables are of many types. For instance, 
R Coronae, in the Northern Crown, is generally of about the 6th 
magnitude, on the fringe of naked -eye visibility, but at irregular 
intervals it drops down sharply, and fades to perhaps the 1 4th 
magnitude. Stars such as SS Cygni and U Geminorum remain 
at minimum for most of the time, but show sudden increases of 
several magnitudes; SS Cygni itself is usually of about magni- 
tude 12, but can rise to above 9. R Scuti, in the tittle constella- 
tion of the Shield, has alternate deep and shallow minima, but 
sometimes loses all semblance of regularity for a while. And Eta 
Argus (now known officially as Eta Carinas*) is completely 
irregular; for a while, between 1837 and 1854, it ranked among 
the most brilliant stars in the sky, but for many years now it has 
remained below naked-eye visibility. On the whole, it is the 
irregular and semi-regular stars which offer the greatest scope 
for amateur observers, if only because one can never tell just 
what they will do next. 

Variable star observations are made by estimating the 
magnitude of the variable as compared with near-by stars of 
known brightness. For instance, Gamma Cassiopeia: is provided 
with two perfect comparison stars in the same constellation, 
Beta (magnitude 2-26) and Delta (2-67). In the case of a 
telescopicjobject, the comparison stars must of course lie in 
the same field as the variable, and a few awkward stars which 
lie aloof by themselves are not easy to estimate properly. 

The first thing to do is to identify the variable. A star atlas is 
necessary, probably together with a chart of type similar to 

* Since the great constellation of Argo has been divided up, Eta Argus has been 
re-christened "Eta Carina;", while Canopus has become "Alpha Carina:". 



those in Appendix XXVIII, and the position of the variable 
can be found. It is, however, a mistake to look directly for the 
variable itself. The best method is to note the stars which will 
be found in the same low-power field, so that an overall impres- 
sion can be built up. Most long-period variables stand out 
because of their redness, but this is never a safe guide, and is in 
any case not valid for the short-period stars and the irregulars. 

It may sound difficult to identify any particular starfield, 
but no two fields are alike, and a little practice will work 
wonders. It is sometimes suggested that the best way is by 
"sweeping about" until the required field comes into view, 
but this is a mistake. When a telescopic variable is to be sought, 
there should be a definite plan of campaign. First identify the 
area by means of naked-eye stars which can be recognized 
without possibility of error, and then proceed by means of 
star alignments and patterns, swinging the telescope north and 
south and in right ascension in terms of a known angular field. 
In difficult cases, an easily recognizable star can be selected 
which has the same declination as the variable, and the telescope 
left stationary until the variable drifts into view (though slight 
adjustments will be needed if the telescope is mounted on an 
altazimuth stand). It is unwise to leave any "safe anchorage" 
for the next until it has been identified with absolute certainty. 
When an observer has once found the field, he will usually 
recognize it again without much trouble, and it can be picked 
up in a matter of seconds, but the approach should always be 
"planned". A moment's carelessness can lead to some very 
peculiar results. 

If the observer belongs to an astronomical society, he can of 
course obtain charts of the fields he needs. Approximate 
positions of some of the long-period and irregular variables 
are shown in the star maps given on pages 264-319. 

There are several methods of making estimations. One 
of the simplest is Pogson's Step Method, in which the observer 
trains himself to gauge a difference of o-l magnitude, which 
constitutes one "step". Suppose that he is observing a variable 
star, and finds that it is two steps fainter than comparison star 
A and one step brighter than comparison star B. He records : 
"A— 2: B+i." He then looks up the magnitudes listed for A 
and B. If A is 80 and B 83, the variable must be 8-a, which is 



two-tenths of a magnitude fainter than 8-0 and one-tenth of a 
magnitude brighter than 8-3. 

A more complex method is the Fractional, used by many 
workers. Here two comparison stars are used, and the brightness 
difference between them is divided mentally into a convenient 
number of parts, after which the variable is placed in its 
correct position in the step-series. If A is the brighter of two 
comparison stars A and B, and the variable is estimated as one- 
quarter of the way from A to B {and hence three-quarters of 
the way from B to A), the record will read: A1V3B. The 
magnitudes of the comparison stars can then be looked up as 
before, and the magnitude of the variable worked out. 

There are many points to bear in mind when using either 
of these methods, and perhaps the most important is that the 
observer should go to his telescope with an open mind. If he 
expects the variable to be of magnitude 7-5, there is a strong 
chance that he will in fact record it as 7-5, whether this is 
correct or not! Neither is it easy to compare a red star with a 
white one. Plenty of practice is needed, but the serious enthu- 
siast will soon find that he has "got the hang of it", after which 
he will be able to estimate many variables during the course of 
a few hours* work. 

One difficulty of observing naked-eye variables such as 
Betelgeux is that a star is bound to be reduced in brightness as 
it approaches the horizon, since it will be shining through a 
thicker layer of the Earth's atmosphere. This "extinction" 
effect can upset an observation completely if it is not allowed 
for, but the table given in Appendix XXIV should help. With 
telescopic observations, extinction can be neglected, since all 
the stars in the field will be at approximately the same altitude 
above the horizon. 

The so-called "secular variables" are of very different type. 
They are stars which seem to have undergone a slow bright- 
ening or fading over the course of centuries. For instance, the 
faintest of the seven stars in the Great Bear, Megrez, used to be 
as bright as its companions, and was so recorded by Ptolemy; 
but it is now a magnitude fainter, though it has been suspected 
of slight fluctuations and is thus well worth watching. Castor, 
one of the famous Twins, is now fainter than Pollux, though it 
used to be brighter; and Theta Eridani, in the River (Map XI), 



has sunk from the first magnitude to the third since the Almagest 
was drawn up. On the other hand Alhena or Gamma Geminor- 
um, not far from Castor (Map V), has brightened up from the 
third magnitude to above the second. Alterations in these stars 
are too slow to be detectable during the course of a life-time, 
and in any case we cannot place full trust in the old estimates, 
but there is always a chance of observing something unexpected. 

If the secular variables are leisurely, the "temporary stars" 
or Novae are nothing of the sort, and are perhaps the most 
violent objects in the entire universe. Occasionally a star will 
blaze up where no star was seen before; it may attain great 
brilliance for a few days or a few weeks, but eventually it will 
fade back into insignificance, becoming so dim that it will be 
hard to see even with a powerful telescope. 

It used to be thought that a nova was really a new star, as 
the name suggests, but this is a mistake. What happens is that 
a normally faint star undergoes a tremendous outburst that 
results in a 70,000- or 80,000-fold increase in brightness. One 
theory held that the flare-up was the result of a collision between 
two stars, but novae are not uncommon (even though few of 
them reach naked-eye visibility), and the stars are so widely 
scattered in space that the idea of frequent stellar collisions is 
quite ruled out. It is now generally thought that a nova is a 
binary system, and that the smaller, more massive star pulls 
material away from its companion; eventually fresh nuclear 
reactions begin in this drawn-off material, and the result is a 
violent but brief outburst. Some nova: develop gaseous 
surrounds of very large size and correspondingly low density. 
If our Sun became a nova, the results from our point of view 
would be decidedly unfortunate, but luckily the Sun seems to 
be refreshingly stable. 

Twenty-three naked-eye novae and many fainter ones have 
been seen during the present century. Pride of place must go to 
Nova Persei 1901 and Nova Aquilae 191 8, each of which 
became brighter than any stars in the sky apart from Sfrius and 
Canopus, but which have by now become very faint telescopic 
objects. Of particular interest was Nova Herculis 1934, which, 
like many other nova, was discovered by an amateur observer. 
It was found on December 13 by J. P. M. Prentice, then 
Director of the Meteor Section of the British Astronomical 



Association, who had been observing shooting-stars and was 
taking a nocturnal stroll after finishing his regular programme. 
The star had an unusually long maximum, and as it faded it 
developed a strong greenish hue, which was most striking with 
the 3-inch refractor that I was using at the time. 

Novas generally appear near the Milky Way zone, but they 
are quite unpredictable, and the increase in light is usually 
so rapid that the amateur sky-watcher has a better chance of 
making the discovery than his professional colleague who is 
busy with a set programme of work. Novas can of course be 
estimated in the same way as normal variables, and it is 
fascinating to watch them as they fall gradually from their 
pinnacle of glory back to the obscurity from which they came. 
Normal novas are spectacular enough, but the rarer "super- 
novae" are even more so. Here the increase in light is much 
greater, and at maximum a supernova may shine as brightly 
as all the other stars in its system put together. In our own 
galaxy, the most famous supernova on record is that of 1572. 
It lay in Cassiopeia, and at its brightest was more brilliant 
than Venus, so that it remained visible in broad daylight. 
Telescopes still lay in the future, so that as soon as the star fell 
below the sixth magnitude it was lost to sight, and it cannot now 
be identified with certainty. However, a certain amount of 
"radio emission" from the area marks die place where the 
supernova once blazed. Another supernova, that of 1054, has 
left a visible cloud of gas which is now called the Crab Nebula, 
and this too is a powerful radio emitter. The only other super- 
novae to be seen in our own system during the past thousand 
years were those of 1006 and 1604. 

Normal bright novas appear only at intervals of years, 
as is shown in the list given in Appendix XXV, but there is no 
harm in the amateur's occupying himself for four or five minutes 
a night in making a naked-eye survey of the Milky Way zone. 
Probably he will never make a startling discovery, but he 
will at least improve his knowledge of the sky, and there is 
always the remote chance that he will achieve lasting fame. 
There have been several naked-eye novae in recent years. In 
1967 George Alcock, who is by profession a schoolmaster in 
Peterborough, discovered a new star in Delphinus, now known 
as HR Delphini. It rose to above the fourth magnitude, and 



remained at maximum for months. The brightest of the recent 
novffi flared up in Cygnus in August 1975. The Japanese were 
the first to detect it (during daylight over Europe), but as soon 
as the sky darkened over England many observers found it 
independently— I did so myself. It had risen very rapidly from 
obscurity to the second magnitude, and on August 30 I 
estimated it as i-8, but it faded very quickly. Generally 
speaking, the amateur has a better chance of discovering a 
nova than the professional who is carrying out a specialized 
programme of research. On the other hand, it must be empha- 
sized that patience is essential. Alcock, for instance, spent many 
years in "learning the sky", until by now he knows the positions 
and magnitudes of 30,000 stars — and can recognize a newcomer 
at once. For his routine searches, he uses a pair of large, 
specially-mounted binoculars. It is also worth noting that 
binoculars are also very useful for ordinary observations of the 
brighter long-period and irregular variables. 

I have already mentioned the red dwarf "flare stars", 
which may brighten up appreciably over a period of a few 
minutes, and fade back to their normal brilliance within the 
hour. Recently they have been the subject of much attention 
by both optical and radio astronomers, and the visual ob- 
servers at the Crimean Astrophysical Observatory have been 
co-operating with the radio astronomers at Jodrell Bank; 
similar work has been carried out in the U.S.A. The trouble 
here is that unless flare stars are kept under continuous watch, 
their outbursts will be missed. All are faint, and generally 
speaking are best studied with photoelectric equipment 
combined with large telescopes. However, it may well be that 
amateurs will be able to make a useful contribution to flare-star 
studies, always provided that adequate instruments are avail- 
able—together with an almost inexhaustible store of patience! 
It is clear that variable stars can give the observer plenty to 
do. There are the red stars of long period, the irregulars with 
their quirks and eccentricities, and the occasional strange 
novse which flare up to unexpected brilliance. The stellar 
heavens are never dull, and there is always something new to 


C/mpter Sixteen 


Some way from Orion, beyond the bright red star Alde- 
baran, can be seen what at first sight looks like a faint misty 
patch. Close inspection shows that this patch is in fact made up 
of stars, one of which is of the third magnitude and the rest 
much dimmer. 

Seven stars can be made out by normal-sighted people, and 
the group is known popularly as the "Seven Sisters",* though 
its official name is the Pleiades. It is a genuine cluster, and not a 
line-of-sight effect. It has been calculated that the odds against 
any chance alignment of the seven most conspicuous stars are 
millions to one against (see Plate XII). 

The Pleiades have been known from very early times, and 
legends about them are found in ancient mythology, but it is 
only during the last three and a half centuries that astronomers 
have realized that there are many similar clusters in the sky. One 
or two can be seen without optical aid ; there are the Hyades 
round Aldebaran, Pr<esepe or the "Beehive" in Cancer, and the 
Sword-Handle in Perseus. Most, however, are too faint to be 
seen without a telescope. 

A pair of binoculars will show the Pleiades very well. 
With a magnification of about 20, the chief stars fill the field, 
and look like jewels gleaming against black velvet. Moreover, 
fainter stars jump into visibility; even a small telescope reveals 
so many that to count them would be a difficult process. The 
Seven Sisters have many junior relatives— over 250, in fact. 

The Pleiad stars look close together, but the cluster is not 
really so dense as might be imagined, though if the Sun lay in 
the middle of the Pleiades our sky would contain many stars 
shining more brightly than Sirius does to us. Nor must we be 
deceived by the fact that the whole cluster takes up only a 
small patch of the heavens, since the real diameter of the group 
is over 15 light-years. Its distance is overdo light-years. 

• Really keen-sighted people can see up to a dozen Pleiads without optical 
aid, but artificial lights make it difficult 10 sec the cluster as anything but a dim 



Almost as famous as the Pleiades are the Hyades, which lie 
around Aldebaran itself, and are shown in Map IV. Actually, 
AJdebaran is not a genuine member of the cluster, as it merely 
happens to lie in the same direction, Telescopically the Hyades 
are not so beautiful as the Seven Sisters, as the stars are much 
wider apart, and it is difficult to get them all into the same 
field of view. Moreover, they are overpowered by the bright 
orange-red light of Aldebaran. 

There is an important difference between the two clusters. 
In the Pleiades, the brightest stars are blue, highly luminous 
giants of type B, whereas in the Hyades the chief members of 
the group are orange giants of type K, B-stars do occur in the 
Hyades, but are much less in evidence. 

Another naked-eye "open cluster" is Pnesepe, shown in 
Map V. It lies in Cancer the Crab, and has been nicknamed 
the Beehive, because in a small telescope it has been said to 
give some impression of a collection of luminous bees. It is 
not prominent without a telescope, and even a half-moon is 
enough to drown it, but it is a fine sight in a small instrument. 

Even more striking arethe twin clusters in Perseus (Map VII), 
marking the "sword-handle" of the legendary hero. To the 
naked eye the only indication of their presence is an ill-defined 
misty patch, but a telescope reveals two rich star-clusters in the 
same low-power field. I have found that a good view is 
obtained with a power of about 30 on a 3-inch refractor. 

Telescopic clusters are numerous, and anyone equipped 
with a small instrument can give himself many hours of enjoy- 
ment by sweeping for them and learning how to pick them up. 
Each has a separate designation, most of the brightest being 
known by their numbers in Messier' s catalogue. Charles Messier, 
it will be remembered, was the French comet-hunter who was 
constantly annoyed by confusing clusters with comets, and so 
drew up a list of objects to be avoided during his searches. Thus 
Praesepe is M.44, the Pleiades M45, and the nebula in Orion 
M.42. The full catalogue, given in Appendix XXVI, contains 
107 objects. A few of the objects listed by Messier cannot 
now be found, and may have been comets that the French 
observer failed to recognize for what they were, 

Praesepe and the Pleiades are open clusters, but some of the 
objects recorded by Messier are of different type. There are for 



instance the globular clusters, which look like compact balls of 
stars, so closely crowded towards their centres that it is difficult 
to distinguish the individual points of light. A rich globular 
may contain a hundred thousand separate stars, and the 
crowding is much greater than in the case of the open clusters. 

All globulars are very remote, and even the nearest of them 
lies at a distance of thousands of light-years. They form a sort 
of "outer surround" to our stellar system, and since the Sun 
is not in the middle of the Galaxy we naturally have a better 
view of the globulars to one side of the sky. Most of them appear 
round the southern constellations of Scorpio and Sagittarius. 

The best way to demonstrate this effect is to imagine that we 
are standing in a woodland glade on a foggy evening. If we 
stand away from die centre of the glade, we can see the 
bordering trees to one side of us, but the trees which mark the 
edge of the glade on the far side will be concealed by the fog. 
If we take each tree to represent a globular, we can understand 
why these strange clusters are best seen in one particular direc- 
tion. Space, too, is "foggy"; there is a good deal of inter- 
stellar dust and gas, and light-waves cannot penetrate it, so 
that in certain directions our view is blocked. 

The globulars are too far away to have their distances 
measured directly, but fortunately they contain RR Lyrae stars, 
and these useful beacons give us the answers at once. As has 
been shown, we can find the distance of an RR Lyne star 
simply by watching how long it takes to pass from maximum to 
maximum, and the distance of the globular in which it lies 
naturally follows. Originally there was some confusion because 
RR Lyrae variables were thought to follow the Cepheid period- 
luminosity law instead of having one of their own, but this 
misunderstanding has now been cleared up. 

The brightest of the globular clusters visible in England is 
M.13, situated in Hercules {Map IX), which is faintly visible to 
the naked eye on a clear night. Binoculars will show it as a hazy 
patch, and a 3-inch will reveal stars near its edges, but to see it 
really well one needs an aperture of from 8 to 12 inches. Then, 
even the centre can be seen to consist of a myriad tiny points, 
and the sight is superb. Oddly enough, M.13 is unusually poor 
in RR Lyras variables. 

Globulars are much less common than the open clusters. 



Only about i oo arc known, and most of these are faint, so that 
Messier listed only 28 of them. Unfortunately for us, the two 
finest globulars, Omega Centauri and 47 Tucanae, lie too far 
south to be visible in England. 

Messier was not really interested in clusters, and regarded 
them simply as nuisances from the cometary point of view, 
so that he listed only those which were liable to confuse him. 
Since his day, many more of the hazy patches have been 
catalogued, until by now the total number runs into millions. 
Herschcl discovered many between 1775 and 1820, and he saw 
that they were of different kinds. Some were obvious clusters, 
but otbers looked more like filmy gas, and these latter were 
termed "nebulae", from the Latin word for "clouds". 

For many years, it was believed that the nebulae were merely 
star-clusters so far away that they could not be resolved with 
the telescopes available. This also applied to the curious 
"planetary nebulae", so called because they showed pale disks 
not unlike those of the planets. But doubts began to creep in; 
some of the nebula: did not look in die least like clusters, and 
their real nature remained dubious. 

By itself, the telescope could not solve the mystery, but the 
spectroscope came to the rescue. In 1864 Sir William Huggins, 
one of the great spectroscopic pioneers, put the matter to the 
test by observing a planetary nebula in Draco, He half ex- 
pected to see a somewhat contused effect due to the result 
of the combined spectra of thousands of stars, but instead he 
saw nothing but a single green line. At once he realized the 
truth. The light of the nebula was made up of one colour only, 
emitted by a luminous gas; the object was not a distant cluster 
at all, but something quite different. 

Diffuse nebulae such as that in Orion's Sword had always 
been regarded as clouds of gas and dust in space ; the planetaries 
too were found to be gaseous, but they are neither planets 
nor nebulae, so that their popular name could hardly be less apt. 
A typical planetary consists of a very faint, very hot Wolf- 
Rayet star associated with an immense "atmosphere" made up 
of incredibly tenuous gas. The low density is not easy to 
appreciate; if we took a cubic inch of air and spread it out over 
a cubic mile, we would arrive at about the correct value. 

The best-known planetary is the Ring Nebula, M.57 



Lyra, close to Vega (Map VIII). It is easy to identify, since it 
lies between two fairly bright stars, the famous eclipsing binary 
Beta Lyne and its neighbour Gamma. A 3-inch telescope will 
show it, but a larger aperture proves that it has the shape of a 
ring, not unlike a faintly luminous motor-car tyre, while the 
central star is only of the fifteenth magnitude. Some of the 
other planetaries are much less symmetrical. 

Planetaries are most interesting objects, and it is a pity that 
most of them are so dim. However, there are plenty of diffuse 
nebulas. A few of them, notably M.42 — the Sword of Orion — 
can be seen with the naked eye. M.42 lies below the three stars 
of the Belt, as shown in Map IV, and cannot possibly be missed. 
It is one of the show-pieces of the sky, particularly as it contains 
the celebrated multiple star Theta Orionis, known commonly 
as the Trapezium because of the arrangement of its four bright- 
est components. M.42 itself is 15 light-years across, and about 
1,500 light-years away. 

Many of these diffuse nebula: are within the range of a small 
telescope, but not all are of the same type. Some, such as the 
nebula contained in the Pleiades cluster, shine simply by 
reflecting the light of the intermingled stars, but others, 
including M.42 Orionis, show spectra which indicate that they 
are shining by themselves; the radiation from the mbced-in 
stars is affecting the gas and making it luminous. Like the 
planetaries, the diffuse nebulae are very rarefied, millions of 
times less dense than our own atmosphere. 

Spectroscopic work has led to our identifying many of the 
gases in nebula:. Hydrogen, helium and oxygen are all present, 
and there are also spectrum fines which were once thought to 
be due to a new element "nebulium", but which have dis- 
appointingly proved to be due merely to oxygen and nitrogen 
in unfamiliar states. 

Diffuse nebulae shine because of the stars contained in them, 
and consequendy a nebula that includes no convenient stai 
will remain dark. Though it will therefore be invisible, it 
will make itself evident because it will blot out the stars or 
luminous gas behind it. Herschel was inclined to believe that 
the occasional well-defined starless patches were true "holes 
in the heavens", but it is now known that there is no basic 
difference between a nebula which shines and one which does 



not. Of the dark objects, the most prominent are the Coal Sack 
in the Southern Cross, unfortunately invisible in England, and a 
section of the Orion Nebula known as the "Horse's-Head" 
because its shape gives the impression of the head of a knight 
in chess. There is also a dark patch on Cygnus, not far from 
Deneb; and several others can be found with small apertures, 
though they are not striking. 

An object that cannot be classed with either the planetaries 
or the diffuse nebulae is M.i, the "Crab Nebula" in Taurus 
(Map IV). This too is bright enough to be seen with a small 
telescope, but a large instrument is needed to show it well. 
The gases in it appear to be expanding from a central point, 
and there is no doubt that the nebula is the wreck of the 
supernova that flared up in the year 1054.. It is one of the most 
powerful known emitters of radio waves, and is also a source 
of X-rays, so that it is unusually interesting. Moreover, it con- 
tains a pulsar. The Crab can be found without much difficulty 
near the third-magnitude star Zeta Tauri, though visually it is 
not spectacular and is easy to overlook. 

In general, a lower power is to be preferred for observing 
nebulae, except for the planetaries ; a magnification of 30 to 40 
on a 3-inch refractor is quite high enough for most purposes. It 
is true that no useful work can be done, but this is no grave 
disadvantage. It is always worth while to relax and enjoy oneself 
among the wonders of the sky. 


Chapter Seventeen 

One of the glories of the night sky is the luminous band 
which is known to everyone as the Milky Way, It stretches 
right round the heavens, and on a clear moonless night it is a 
magnificent spectacle. 

Galileo's first telescope, applied to the sky in the winter of 
1609-10, led him to say that the Milky Way is made up of 
"an infinite number" of stars. This is an exaggeration; the 
stars are not infinitely numerous, but there are about one 
hundred thousand million of them in our own system, together 
with a vast quantity of interstellar material. 

Sweeping the Milky Way with binoculars or a low-power 
telescope will reveal so many stars that to count them by ordin- 
ary methods would take more than a lifetime. The belt is 
fairly well defined, and its stars seem to be bunched closely 
together, giving an impression of extreme over-crowding. But 
the universe is not a crowded place, and the stars in the Milky 
Way are no more packed than those in the rest of the sky. The 
luminous band itself is nothing more than a line-of-sight effect, 
due to the way in which our star-system or Galaxy is shaped. 

A rough diagram of 
the Galaxy is given in 
Fig. 61. The stars are 
arranged in a form which 
bears some resemblance 
to two plates clapped 
together by their rims, 
with the Sun (S) well 
away from the centre. 
The dimensions of the 
"plate" are known with fair certainty, and the diameter (AB) 
proves to be 100,000 light-years, with the greatest breadth of it 
only one-fifth of this. We can now understand the reason for 


Fig. 61. Position of the Sun (S) in the 
Galaxy. Looking along the main plane 
(AB) results in the Milky Way effect. 


the Milky Way effect. When we look along SA or SB, we see 
many stars almost in the same line of sight, but when we look 
along SC or SD there arc far fewer objects to be seen. 

Actually, it is not possible to see all the way from S to B. 
In the main plane of die Galaxy there is a great deal of obscur- 
ing material, both dust and gas, and starlight cannot penetrate 
it any more than a car's headlamps can penetrate a thick fog. 
The centre or nucleus of the galaxy lies in the direction of the 
rich star-clouds in Sagittarius (Map VIII), and here we have 
some glorious telescopic fields, but what lies beyond these 
fields can never be seen. Fortunately, the new science of radio 
astronomy has come to our rescue. Radio waves are not blocked 
by the interstellar matter, any more than a man's voice is 
blocked by fog, and we are at last learning more about the 
core of our stellar system. 

Radio astronomy has also helped us to find out something 
about the structure of the Galaxy. It proves to be spiral, not 
unlike a vast Catherine-wheel, and the whole system is in 
rotation round its centre. The Sun takes about 225 million years 
to complete one circuit, so that it has been round only once 
since the far-off times when the Coal Measures were being laid 
down in the period of Earth history known to geologists as the 
Carboniferous. But though the Sun is moving round the centre 
in an almost circular orbit, other stars have paths of different 
types. It has now been established that there are two distinct 
"families" of stars, known generally as Populations I and II. 

Population I stars, such as the Sun, are found in the spiral 
arms of the Galaxy, They are of various spectral types, but 
the most luminous of them are Blue Giants. On the other hand 
the senior members of Population II are Red Giants of vast 
size and relatively low temperature. Population II stars are 
found in the nucleus of the Galaxy, and also penetrate the 
vacant spaces between the spiral arms, while the stars of 
globular clusters also belong to this type. Since some Population 
II objects are revolving more slowly round the nucleus, and in 
more elliptical orbits, they seem to have high velocity with 
respect to ourselves, just as a slow-moving push-bicyclist will 
seem to have "high velocity" relative to a stream of cars which 
is moving steadily as a group. 

It is also interesting to note that in Population II areas, 



there is less of the cosmic obscuring matter which is such a 
nuisance to us. The areas have in fact been "swept clean", 
but in Population I regions the Blue Giants are always associ- 
ated with clouds of dust and bright gaseous nebulae. 

It is pointless to say much about methods of observing the 
Milky Way, except to repeat that a low power is to be preferred 
unless some particular object such as a faint nebula is to be 
examined. There are innumerable rich star-fields, particularly 
in the Cygnus area and in Sagittarius, and one never tires of 
sweeping about in these glorious regions, even though the 
chances of making a useful discovery are very small. 

Two of the most striking of the objects in southern skies are 
the Clouds of Magellan, or Nubecula?. There are two of them, 
one much more conspicuous than the other, and it used to be 
thought that they were detached portions of the Milky Way; 
but it is now known that they are separate star-systems, and 
they may probably be regarded as "satellites" of our Galaxy. 
Each is concentrated towards its centre, while in the case of the 
Large Cloud there are vague indications of a spiral structure 
(Map XV). 

Both Clouds are prominent naked-eye features, and contain 
hundreds of thousands of observable stars. Fortunately some of 
these stars are Cepheids, which have made distance estimations 
possible. In the Large Cloud, Blue Giant stars are common, 
and there is also much dust and nebulosity, so that the 
population appears to be mainly of Class I. Here too lies one 
of the most luminous stars known, the remarkable variable S 
Doradus, which is the equal of a million Suns and yet is so 
far away that we cannot sec it at all except by using a telescope. 
It would take many pages to describe all the various features 
to be found in the Clouds ; they are superb objects, and it is a 
great pity that they can never be seen from European latitudes. 

Vast though they are, the Clouds are far smaller than the 
system in which we live. Until recentiy it was indeed thought 
that the Milky Way was the largest of all galaxies, so that it 
had a special status in the universe, but this is far from being 
the case. There are millions of galaxies within range of our 
telescopes, and there is no longer any reason to suppose that 
our own system is of exceptional size. 

There is still a tendency to refer to the galaxies as "spiral 



nebulae", but this is a bad term. Not all the galaxies are spiral, 
and certainly none of them is a nebula in the proper sense of 
the word, though they do contain nebulae of the same type as the 
Sword of Orion, as well as open clusters and globulars. 

The nearest of the major galaxies, M.31, is easily found, 
since it can be seen with the naked eye. It lies in Andromeda, 
and is shown in Map VII. For many years it was thought to lie 
inside our own system, even though its spectrum showed that it 
was made up of stars and was not a luminous gas-cloud; but 
there were also suspicions that it might he outside the Milky 
Way altogether. The riddle was solved in 1923, when Cepheids 
were discovered in the spiral arms. These Cepheids proved 
to be so remote that M.31 could no longer be regarded as a 
member of our Galaxy, and a first estimate of its distance gave a 
value of 900,000 light-years. 

Other Cepheids were found, and in 1944 a correction was 
made which reduced the distance of the galaxy to 750,000 light- 
years. All seemed to be well, but in 1952 stellar astronomers 
had a rude shock. It was found that the Cepheid scale was 
badly in error, because the difference between Population I 
and Population II Cepheids had not been realized; the result 
was that the whole distance-scale of the outer universe had to be 
doubled. Instead of lying at a mere 750,000 light-years, the 
Andromeda Galaxy was a million and a half light-years away. 
Further investigations have increased this still more, and the 
latest estimate is 2,200,000 light-years. The light now entering 
our eyes started on its journey towards us before the beginning 
of the last Ice Age. 

It also followed that instead of being smaller than the Milky 
Way, the Andromeda Galaxy is larger, with a total mass at 
least 1 1 times as great. It too is in rotation; it too has its 
Population I stars (mostiy in the arms) and Population II stars 
(mainly in the nucleus), as well as globulars, open clusters, 
gaseous nebula: and even two satellite galaxies of the same 
status as our Clouds of Magellan. Novae have been observed, 
and in 1885 there was even a supernova which flared up to the 
sixth magnitude. At maximum it could only just be seen with- 
out a telescope, but had it appeared inside our own Galaxy it 
would probably have shone in our skies more brilliantly than 



The Andromeda Galaxy is spiral, but as it is not face-on 

to us the spectacular Catherine-wheel effect is largely lost. 
I have always regarded it as rather a disappointing object in 
a small telescope, and in a 3-inch refractor it looks like a badly- 
defined patch of mistiness. Powerful telescopes are needed to 
show it really well, but the best results are obtained by means 
of photography. In recent years, radio waves emitted by the 
galaxy have also been detected. 

Other galaxies are better presented, so that they appear as 
Catherine-wheels. In some cases, however, there is no 
spiral structure. A few galaxies (such as the Small Cloud of 
Magellan) are virtually formless, while others are elliptical 
or globular. It used to be thought that the different shapes of 
galaxies indicated different stages in evolution, but this 
plausible-sounding idea has now been rejected by most 
astronomers. There is much that we do not know. For instance, 
the cause of spiral structure is still very much of a mystery. 

Galaxies are apparently most numerous away from the 
Milky Way zone. This does not mean that there is anything 
lop-sided about their distribution; the effect is due purely to 
the obscuring matter near the galactic plane (AB in Fig. 61). 
There are groups of galaxies here and there, and the total 
number of known external systems is staggeringly great, 
though even the giant telescopes of to-day cannot show us 
more than a small part of the universe. 

Spectra of galaxies are not particularly easy to study. Each 
is made up of the combined spectra of millions of bodies of all 
types, and the result is bound to be much less clear than with a 
spectrum of a single star. However, one thing has become clear: 
nearly all the spectra of galaxies show a red shift, which indi- 
cates a velocity of recession. 

Apart from the Andromeda Spiral, the fainter spiral in 
Triangulum, the two Nubecula^ and more than twenty minor 
systems which make up our own "local group", all the galaxies 
are racing away from us, and the more distant they are the 
faster they go. For instance, the remote galaxy 3C-295 in 
Bootes seems to be about 5,000 million light-years away, and 
to be receding at almost half the velocity of light. 

If we accept this principle, we must conclude that the whole 
universe is expanding, with every group of galaxies racing 



away from every other group. The red shifts do not indicate 
that our own particular area is any way exceptional ; the situa- 
tion may be visualized by picturing a balloon filled with 
coloured gas — when the balloon is burst, the gas expands, each 
part of it receding from each other part. The analogy is ad- 
mittedly not very accurate, but it is the best that can be done. 

There are some astronomers who doubt whether the red 
shifts in the spectra of galaxies are due to the ordinary Doppler 
effect. If there is another explanation, the whole idea of an ex- 
panding universe might have to be drastically revised. This is 
not likely, but neither is it impossible— and of late there have 
been startling developments, due in the main to the new science 
of radio astronomy. 

There are some galaxies which are remarkably powerful 
radio sources. One such object if Gygnus A, which is so dim 
optically that giant telescopes are needed to show it at all. It 
apparently lies at a distance of some 200 million light-years, 
but even so it is one of the strongest radio sources in the sky, 
and the cause of this emission is still not known with any 
certainty at all. A few years ago there was a highly plausible 
theory, according to which Gygnus A and others of its kind 
were made up of two galaxies which were in collision, and were 
"passing through" each other in the manner of two orderly 
crowds moving in opposite directions; the individual stars 
would seldom or never suffer direct hits, but the interstellar 
matter would be colliding all the time, so producing the radio 
emission. This sounded most satisfactory, but it was then found 
that the process was hopelessly inadequate to account for the 
remarkable power of the radio waves, and the whole idea of 
colliding galaxies had to be cast upon the scientific scrap-heap. 
Unfortunately, nobody has yet provided a substitute theory 
which is any better. We do know, however, that there are 
radio-emitting galaxies which show evidence of having under- 
gone violent explosions in their central parts. 

In 1963 there was a new development. By then, many radio 
sources had been tracked down, and identified either with 
galaxies, supernova remnants or other known objects. However, 
some sources seemed to coincide in position with stars. One, in 
particular — the source known by its catalogue number of 
3C-273 — coincided with what seemed like a rather faint bluish 



star, which had been recorded photographically often enough. 
The whole situation seemed peculiar, and when the radio 
astronomers asked the American optical astronomers to take a 
closer look at the spectrum of the "star", some amazing facts 
emerged. The main surprise was that the bluish object was not 
a star at all. It had a totally different kind of spectrum, and a 
tremendous red shift, which presumably meant that it was very 
remote and was receding very rapidly. This was the first- 
identified of the objects now known as quasi-stellar objects or, 
more commonly, as quasars. 

The first quasar would have to lie at a distance of about 
1 ,500,000,000 fight-years, assuming its red shift to be a normal 
Doppler effect. Yet it was stellar in appearance — and the final 
result was that if it were as remote as this, and shining with the 
magnitude measured by ordinary visual methods, the lumin- 
osity must be equal to 100 whole galaxies put together! Since 
the quasar was clearly much smaller than a galaxy, in view of 
its starlike aspect, this conclusion seemed to make no sense at 
all. Nobody could imagine how so small an object could be 
radiating so much energy; and let it be admitted that the 
problem is still as baffling as ever. Other quasars were soon 
identified, some of them still farther away than 3C-273 and 
receding even more rapidly. 

Quasars are, on the whole, the most remarkable objects ever 
found in the sky. If they are as distant as their red shifts indicate, 
they must be drawing upon some energy-source about which 
we know nothing at all. All sorts of ideas have been put 
forward, such as the production of energy from the gravitational 
collapse of what may be termed a "super-star", but we are still 
very much in the dark, and all we can do is to await the results 
of further research. 

These are fascinating problems indeed, but to discuss them 
at all fully would be beyond the scope of a book devoted to the 
needs of the amateur astronomer equipped with a modest 
telescope. Yet the detection of the quasars shows us how little 
we really know, and it is not impossible that our whole idea 
of the make-up of the universe may have to be altered during 
the next few years. 


Chapter Eighteen 


Only a few centuries ago, the world was believed to be of 
fairly recent formation. Archbishop Ussher of Armagh summed 
matters up in 1654, when he stated categorically that the Earth 
came into being at nine o'clock in the morning of October 26, 
4004 b.g. Nowadays we know that the problem is not so simple 
as this, and that die Earth is well over four thousand million 
years old, while the Sun is presumably older still. 

The Sun must have been formed from material in the 
Galaxy, but when we come to consider how the universe itself 
was created we run up against a blank wall. There are plenty 
of theories, but most of them start from the assumption that 
matter was created at a definite moment in time, which is not 
particularly helpful in view of the fact that we do not really 
understand what "time" is. The Belgian mathematician 
Lemaitre believed that the universe was once concentrated in a 
single giant radioactive atom, and that time and space began 
when this blew up; according to other theories, the original 
universe consisted of a mass of diffuse gas distributed uniformly 
throughout all space. Whether we adopt the "big bang" or the 
quieter creation, we are still none the wiser. However far back 
we go, we can always picture a still earlier period. The only 
way to try to solve the problem is to use the language of 
very abstruse mathematics, but even this leads us into a blind 

At all events, there must have been a time when there 
were no galaxies. Presumably the galaxies condensed out of 
the widely-spread material, and in turn the stars condensed 
out of the galaxies. We are still very uncertain about the exact 
way in which a star is born, but there is little doubt that 
nebular matter is responsible, and it is possible that some of the 
stars inside the Orion nebula are true celestial infants. 

When we come nearer home, we are slightly more confident 
of our facts. However the planets were formed, the Sun was in 
some way responsible. It used to be thought that the bodies of 



the Solar System were thrown-off pieces of the Sun itself, 
probably drawn off by the tidal pull of a passing star, but this 
idea has now been abandoned, so that an alternative mode of 
formation must be sought. Sir Fred Hoyle once suggested that 
the planets are the result of the supernova disruption of a 
former binary companion of the Sun, but it is now generally 
agreed that the planets were formed from a cloud of dust and 
gas associated with the young Sun— a kind of "solar nebula", 
in fact. The planets built up by accretion, and the process was a 
relatively slow one. 

So much for the past; but what lies ahead ? Will the universe 
last for ever, or will it finally die, so that nothing remains but 
dead, lifeless bodies scattered through space? 

Here again we have to admit that we simply do not know. 
If we suppose the universe to be eternal, then we have to picture 
a period of time which has no ending; if not, then we must 
concede that "time" itself comes to an end, which is equally 
beyond our mental powers. 

In the late 1940's a group of astronomers at Cambridge, 
headed by H. Bondi and T. Gold, advanced a new and daring 
idea. They supposed that the universe has always existed, and 
will exist for ever; as old stars and galaxies die, matter is 
spontaneously created out of nothingness, so that new galaxies 
can be produced. Of course, there was no suggestion that a 
fresh galaxy would suddenly appear in recognizable form. The 
rate of creation of new matter would be too slow to be detect- 
able, any more than it would be possible for us to detect a new 
sand-grain in the whole of the Sahara Desert. 

According to this theory, modified later by Hoyle, the 
universe would be in a steady state, and must always have 
looked much the same as it does now; there would be the same 
numbers of galaxies, even though the individual galaxies 
would not always be the same. It is an attractive idea, but 
unfortunately it has not stood up to careful investigation. 

Consider the two rival theories — the evolutionary or "big 
bang", and the steady-state. On the first hypothesis, the matter 
in the universe was once more closely packed than it is now; 
on the second, the average distribution has always been the 
same as at present. If we could go back in time, and see the 
universe as it used to be thousands of millions of years ago, we 



would have something definite to guide us. Closer packing 
of the galaxies would favour evolution; no change in the 
distribution of the galaxies would support the steady-state idea. 

We cannot achieve time-travel, but we can do something 
almost as good. When we examine a galaxy at a distance of 
(say) 5,000 million light-years, we are seeing it as it used to be 
5,000 million years ago; in other words, we are looking back 
into the past. The method, then, is to study the distribution of 
very remote galaxies, and see whether they are more closely 
crowded than the systems nearer at hand. 

Optical telescopes cannot reach out far enough, but radio 
telescopes can probe farther. Work by Sir Martin Ryle at 
Cambridge has shown that the distribution of remote galaxies 
is not the same as with the closer parts of the universe, and it 
now seems that the steady-state theory must be given up, at 
least in its classical form. It has now been rejected by almost 
all authorities, albeit with considerable reluctance. 

On the other hand, this does not prove that the universe 
began with a "big bang" and is now evolving toward eventual 
death. It has been suggested that the universe is in an oscillating 
condition, and that the cycle has been repeated many times. 
At present, the galaxies are in a state of spreading-out 
(assuming, of course, that we accept the evidence of the red 
shifts in their spectra), but it may be that in the future this 
mutual recession will cease, and that the galaxies will come 
together once more before embarking upon a new phase of 
expansion. But we are still uncertain of our ground, and the 
discovery of the quasars has shown again how little we really 
know. Quasars, indeed, may provide us with vital clues, 
since all the current evidence indicates that they really are the 
most powerful and the most remote objects known to us. Far 
from saying the last word, we cannot be sure that we have said 
even the first. 

It seems that our own galaxy, at least, must die; but men of 
the Earth will have vanished from the scene long before the end of 
the story. The Sun will eventually become more luminous, and 
there must come a time when our world will be too hot to 
support life. Even if it is not destroyed, it will become a scorched 
globe devoid of air and water, and all living creatures will have 
perished from its surface. 



There is no immediate danger. The crisis will not come for at 
least five thousand million years, and by that time conditions 
will in any case be so different that it is pointless to speculate 
about them. Mankind may have destroyed itself by atomic 
warfare ; it may simply have died out, just as the great reptiles 
vanished over seventy million years ago; or it may be so 
altered in form that to ourselves it would seem wholly alien. 
At best, it may have learned so much that our remote descend- 
ants will be able to save themselves by abandoning their home 
world and migrating to another planet. 

Of course, this is nothing more than fantasy. Our brains are 
not able to appreciate such a time-span, and we must accept 
our limitations. We are creatures of the present; the universe 
in which we five is spread out for inspection, and everybody 
can play a part, from the observer who photographs galaxies 
with the Palomar reflector down to the humble amateur who 
studies the Moon with the aid of a portable telescope set up in 
his back garden. 


Appendix I 


Distance from Sun, in 
Planet millions of miles 

Max. Mean Mist. 








JggJ MMMb 










93 'a 
141 -5 



91 -4 
1 28 -5 

88 days 

=34-7 .. 
365 .. 
687 „ 
1 1 -86 years 

sg-4 6 .1 
8401 „ 

1,867 ". 783 '.699 

2,817 2.793 a»769 I64-79 

4,566 3,666 2,766 247-70 



58d. 5h. 
23h. 56m. 
24h. 37m. 33a. 
9b. 50m. 30s. 
1 oh. 14m. 

369-7 About 23b?. 
367-5 About 22h.* 
366-7 6d. oh. 


Diameter in 


Apparent Diameter 
seconds of arc 
Max. Mi*. 





Mass Vri. 



13-g 4-5 






66-o g-6 

— 4-4 






— — 







25-7 3-5 

— 2-8 






50-1 30-4 







20*9 15-0 







37 3-i 

+ 5'6 






2*2 2-0 







o-3(?) 0-3{?) 






Appendix II 



ffSTftJT. Sidereal Period Diameter, Maximum 







2,160 - 







~ 10 











Amalthea (V) 













Europa fll) 







Ganymede (HI) 






Callisto (IV) 







Leda (XIII) 





Himalia (VI) 


2 5* 



Lysithea (X) 




1 8-6 

Elara (VII) 





Ananke (XII) 





Carme (XI) 





Paslphae (VIII) 




1 8-8 

Sinope (IX) 

1 4.725 




(Satellite XIV, reported by C. Kowal, has not yet 

been confirmed.) 










I a pet us 




9 2 ° 

























1 2- 1 

1 1 -6 






* Denotes retrograde motion, 



Mean dist.from 
centre of primary 
Thousands of miles 

Sidereal Period 

d. h. m. 

Diameter, Maximum 
mitts Mag. 













9 5° 

12 29 

3 28 

16 56 

11 7 











3.5 00 





♦ Denotes retrograde motion. The diameter* and magnitudes of the fainter 
satellites are most uncertain, and different authorities give different values. For 
instance, the following diameter estimates are adopted in the Handbook of the British 
Astronomical Association: Io 2,000 miles, Europa 1,800, Ganymede 3,100, Callisto 
a,8oo, Titan 3,000, Triton 2,300, Iapctus only 700, All we can really say is that, 
generally speaking, the values are of the right order. 

Appendix III 


The followino list includes data for the first ten minor 
planets to be discovered. Objects with interesting orbits, such 
as the Trojans and the "Earth-grazers", are in general too 
faint to be seen with amateur-owned equipment. 




Sidereal Period 

mean uist.jron 

Sun, millions 

of miles 

1 VrfllKB 

deg. min. 














257 4 







































3 68 
























5 59 






Appendix IV 


Mercury, 1978-1985 

Eastern elongation (evening star) : 

1978 Mar. 24, July 22, Nov. 16. 

1979 Mar. 8, July 3, Oct 29. 

1980 Feb. 19, June 14, Oct. 11. 

1 98 1 Feb. a, May 27j Sept. 23. 

1982 Jan, 16, May 8, Sept. 6, Dec. 30. 

1983 Apr. st, Aug. 19, Dec. 13. 

1984 Apr. 3, July 31, Nov. 25. 

1985 Mar. 17, July 14, Nov. 8. 

Western elongation (morning star) : 

1978 Jan. ii, May 9, Sept. 4, Dec. 24. 

1979 Apr. 21, Aug. 19, Dec. 7. 

1980 Apr. 2, Aug. 1, Nov. 19, 

1981 Mar. 16, July 14, Nov. 3. 

1982 Feb. 26, June 26, Oct. 17. 

1983 Feb. 8, June 8, Oct. t. 

1984 Jan. 22, May 19, Sept. 14. 

1985 Jan. 3, May I, Aug. 28. 

Transits of Mercury will occur on 1986 Nov. 13, 1993 Nov. 6 and 
1999 Nov. 15. 



Venus, 1 978-1985 

1978 Jan. 22 Superior conjunction. 
Aug. 29 E. elongation. 

Nov. 7 Interior conjunction. 

1979 Jan. 18 W. elongation. 
Aug. 25 Superior conjunction. 

1980 Apr. 5 E. elongation. 
June 15 Inferior conjunction. 
Aug. 24 W. elongation. 

1 98 1 Apr. 7 Superior conjunction. 
Nov. 1 1 E. elongation, 

1982 Jan. 21 Inferior conjunction. 
Apr. 1 W. elongation 

Nov. 4 Superior conjunction. 

1983 June 16 E. elongation. 
Aug. 35 Inferior conjunction. 
Nov. 4 W. elongation. 

1984 June 15 Superior conjunction. 

1985 Jan. 22 E. elongation. 

Apr. 3 Inferior conjunction. 
June 13 W. elongation. 

The next transits of Venus will be on 2004 June 7 and 2012 June 4, 
after which there will be no more until 2117 December 10 and 
2125 December 8, 


Appendix V 





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All Earth-based observations of Mars have now been super- 
seded by the space-probe results, but it is still interesting to give 
a map showing the features visible with modest telescopes. 

The map given here is based upon my own observations, 
made during 1963. The opposition of 1963 was, of course, 
rather unfavourable, but at least Mars was well north of the 
equator; the planet's northern hemisphere was tilted toward us. 
The polar cap was much in evidence, and there were various 
short-lived cloud phenomena here and there on the disk. 

I do not claim that this map is of extreme precision ; it 
is not intended to be. What I have done is to put in the 
features that I was able to observe personally, making the 
positions as accurate as possible, and taking care to omit 
everything about which I was not fully satisfied. I have 
retained the old (IAU) nomenclature, though it is now being 
revised and will soon become obsolete. 

Some of the Martian markings are very easy to observe. In 
1963 I was able to see various dark features with a 3m. re- 
fractor, without the slightest difficulty; most prominent of all 
are the Syrtis Major in the southern hemisphere and the Mare 
Acidalium in the northern, though Sinus Sabaeus, Mare Tyr- 
rhenum and other dark areas are also clear. The more delicate 
objects require larger apertures; I doubt whether, in 1963, 
Soils Lacus could have been glimpsed with anything less than 
an 8|in. reflector, though it is of course possible that a 6in. 
would have shown it to observers with keener eyes than mine 

Obviously, not all the features shown here are visible at any 
one moment. The map was compiled from more than fifty 
separate drawings made at different times. Elusive features 
which were marked as "suspected only" have been omitted. 
Since the chart is drawn to a Mercator projection, the polar 
regions are not shown, but this does not much matter — the 
south pole was badly placed (indeed, the actual pole was 
tilted away from the Earth), while the north polar region was 
covered with its usual white cap, which shrank steadily as the 
Martian season progressed. 

No doubt many observers using the same instruments would 
have seen more than I did. All I will claim is that my rough 
map, unlike some other published charts, does not show any 
features which are of dubious reality ! 


Appendix VI 








diameter, * Mag. Constellation 


Tan, 22 
Feb. 25 

14*3 -i'i Gemini/Cancer 


13*8 -i-o Leo 


Mar. 31 

14-7 -1 -a Virgo 


May n 

17-5 -i-8 Libra 


Opposition date Constellation 


Jan. 24 



Feb. 24 



Mar. 26 



Apr. 25 
May 27 





June 29 



Aug. 4 




Feb. 16 



Mar. 1 

Leo (Rings edge-on three 


Mar. 13 

Leo times, 1979-80.) 


Mar. 27 



Apr. 8 

Virgo (N. face of rings on view) 


Apr. 21 



May 3 



May 15 


Appendix VII 


Great Red Spot 


Nomenclature of Jupiter 

The diagram shows the main belts and zones: 

SPR = South Polar Region 

SSTZ = South South Temperate Zone 

SSTB = South South Temperate Belt 

STZ <m South Temperate Zone 

STB = South Temperate Belt 

STrZ = South Tropical Zone 

SEB = South Equatorial Belt 

Eq. Z = Equatorial Zone 

Eq. Band = Equatorial Band 

NEB = North Equatorial Belt 

NTrZ = North Tropical Zone 

NTB = North Temperate Belt 

NTZ <= North Temperate Zone 

NNTB — North North Temperate Belt 

NNTZ = North North Temperate Zone 

NPR = North Polar Region 



^ The following is a typical extract from my own observation 

1963 November 4, 12 1-inch reflector. Conditions very variable. 

Feature Longitude 

Ststem I System If Remarks 

l82U X360 








c. of white spot in STZ 
f. of this white spot 
c. of white patch on the Equator 
p. of visible section of NTB 
f. of the white patch on the Equator 258-9 
f. of dark mass on N edge of NEB 263-1 
(c= centre, p= preceding, f= following) 

To work out the longitudes of the features, use the tables 
given in the B.A.A. Handbook, which give the longitude of the 
central meridian for various times. 

Example, The 19.57 transit of the centre of the white spot in 
the STZ. From the tables: longitude of the central meridian 
(System II) for i6h on November 4 is 038-9. This is 3I1 57m 
earlier than the time of the transit. Therefore, the longitude for 
1 9.57 may be worked out from the second table in the Handbook : 

Long at i6h. Nov. 4: 

+ 3h 

+ 50m 

+ 7m 

= + 3I1 57m 


1 08 -8 

30 -2 



If the calculated longitude works out at over 360, 
subtract 360 . 

It is important to use the correct System; System I is bounded 
by the N edge of the SEB and the S edge of the NEB, all the 
rest of the planet being System II. If the wrong tables are used, 
the results can be very peculiar indeed, since Systems I and II 
differ by many degrees. 

Even more convenient tables are given in B. M. Peek's 
admirable book, The Planet Jupiter, and the example may then 
be worked as follows : 

c vvui&cu a» lOUWWS. 

Long, at i6h, November 4 (from the Handbook) 
+ 3 n 57»« (from Peek's tables) 

= 0389 
- 143 ' g 



Appendix VIII 


Definite features on the disk of Saturn are so rare that 
our knowledge of the rotation periods of the different zones 
is not nearly so complete as in the case of Jupiter. 

Valuable work can however be done in estimating the bright- 
ness of the different zones, as well as of the rings, as these are 
suspected of variation. The scale adopted is from a value of 
(brilliant white) to 10 (black shadow). In general, Ring B is the 
brightest feature, and the outer part has a brightness of 1. 

The easiest way of recording is to prepare a sketch (perhaps 
a rough one) of the globe and rings, and then merely jot down 
the numerical values upon the drawing itself. It is best to make 
each estimate twice; first, start from the darkest feature and 
work through to the lightest, then begin once more, this time 
with the lightest feature, whicb is almost always the outer 
part of Ring B. The following is an extract from my own 
notebook : 

1956 May si, oh. to oh. som. i2i-in. Refl. X 460. Conditions good. 

N.E.B, intermediate zone = 5$ 
N. Equatorial Belt, N. 

component = 6j 

Encke's Division = 7 

RingC = 7 

Cassini's Division = 7l 

Shadow, Rings on Globe = 8 

Shadow, Globe on Rings = 8£ 

Ring B, outer = 


Ring B, inner wm 


Equatorial Zone = 


N. Temperate Zone = 


N. Polar Region = 


N. Temperate Belt = 


Ring A = 


N.E. Equatorial Belt, 


component = 


Of course, the different 

seen individually when the 

parts of the ring-system cannot be 
rings are edge-on to us, as in 1 966. 


Appendix IX 


(l) LUNAR ECLIPSES, I978-I985 

In the table, an asterisk denotes that the eclipse is total. 
The last two columns show whether or not the eclipse can be 
seen in England and in the U.S.A. : "partly" may mean that 
the Moon is very low in the sky, or that the Moon rises or seta 
while the eclipse is in progress. 

Ttar DqH 


Pifctntagt of Virihlc in 

eclipst, A. 

Moon edipstd Englaru 


1978 March 24 





1978 September 16 





1979 March 13 





1979 September 6 





1981 July 17 





1982 January 9 





1 982 July 6 





1982 December 30 





1983 June 25 





1985 May 4 





1985 October 28 






(2) SOLAR ECLIPSES, I 978- I 985 

Partial; Antarctic area. 

Partial ; Arctic area. 

Total for 3 minutes in the Hudson's Bay area of 

Annular for 6 minutes in Antarctica. 
Total for 4 minutes in parts of the East Africa area. 
Annular in South Pacific, Brazil, etc. 
Annular: Pacific, S. Australia, New Zealand. 
Total for just over 2 minutes in parts of the USSR and 

N. Pacific. 
Partial : Antarctic area. 
Partial : Antarctic area. 
Partial : Arctic area. 
Partial : Arctic area. 
Total for 5 i minutes in parts of Indian Ocean and 

Annular; Adantic, Central Africa. 
Annular; Mexico, parts of USA, Adantic, N. Africa. 

Total for almost 2 minutes in parts of the S. Pacific. 

Partial : Arctic area. 

Total for over if minutes: S. Pacific, Antarctica. 

The next total eclipses visible from anywhere in Britain will be on 
1999 Aug. 11, 2090 Sept. 23, and 2135 Oct. 7. 

There will be partial eclipses visible from Britain on 1994 May 
10 (i8h GMT) and 1996 Oct. 12 {14I1 GMT). Only in the 1996 
eclipse will the Sun be more than half covered by the Moon. 

1978 Apr. 

1978 Oct. 

1979 Feb. 




J 979 Aug. 
1980 Feb. 

1980 Aug. 

1 98 1 Feb. 
1 98 1 July 


1982 Jan. 25 
1982 June 21 

1982 July 20 
ig82 Dec. 15 

1983 June 11 

1983 Dec. 4 

1984 May 30 
1984 Nov. 22 

1985 May 
1985 Nov. 



Appendix X 


Many artificial satellites are now in orbit round the Earth. 
Some are so far above the ground that they will remain aloft 
indefinitely, since they are more or less unaffected by atmos- 
pheric drag; others will decay much more quickly. And, of 
course, many satellites of the Russian Cosmos series are brought 
down deliberately. By mid-1978, over 1000 Cosmos vehicles had 
been launched. Oddly enough, some of the most famous and 
important satellites have been much too faint to be seen with 
the naked eye — notably Telstar, the first of all successful com- 
munications satellites, which is still in orbit even though its 
power has long since failed. On the other hand the two U.S. 
balloon satellites, Echo I and Echo II of the 1960s, were much 
too bright to be overlooked by even a casual observer. 

There are various ways of keeping track on a satellite. If the 
vehicle has a transmitter on board ("active satellite") it can of 
course be tracked by radio; and most satellites can be detected 
and measured by radar, though admittedly there are a few 
materials which are hard to detect in this way. I do not propose 
to say more about these methods here, because they are beyond 
my scope — though it would be ungenerous not to mention the 
boys of Kettering Grammar School, who, under the guidance of 
their science master (Mr. Perry) have an amazing record in 
picking up radio signals from satellites of all kinds. 

Photographic cameras, such as the Baker-Nunn and the 
Hewitt, coBt a great deal of money. An ordinary camera can of 
course be used to record the trail of a bright satellite, but this is 
really a matter of personal interest rather than anything else. A 
typical trail is shown in Plate XIV. 

Visual satellite-spotters have done valuable work, and still do. 
Remember that the orbits of satellites are always changing, 
because of the effects of air-drag. The orbits cannot be predic- 
ted ahead with real accuracy, and this is why visual observations 



are needed. If the position at any definite time is known, the 
observation can be used to make a correction to the orbital 

What has to be done, then, is to make an accurate estimate of 
the satellite's position, making sure that the timing is correct to 
o-i second or so. A split-action stop-watch is a virtual necessity. 
Stars are used as reference-points; the moving satellite may be 
timed at the moment when it passes half-way between two 
identifiable stars, or perhaps when it makes up a triangle or 
some other definite configuration with two stars. It is not often 
that a satellite occults a star, though of course it does happen 

Bright satellites may be tracked with the naked eye, but most 
require optical aid. Binoculars are ideal for this purpose, though 
some observers use wide-field telescopes. Let it be stressed that 
an ordinary astronomical telescope used for lunar or planetary 
work is not suitable, because the field will be too small and the 
telescope will not be manoeuvrable enough to swing about 

It is pointless to go out at night, sweep around the sky and 
hope to find a moving satellite ! Predictions must be obtained ; 
these are supplied to serious observers by the B.A.A. Artificial 
Satellite Section. The method is to go outside well before the 
satellite is expected, and keep watch on the area through which 
it will pass. When it appears, it can therefore be timed as it 
passes through or near a group of suitable stars. 

I am not an observer of artificial satellites, and I do not there- 
fore feel qualified to say much about them here; but excellent 
books are available, and above all there is Observing Earth 
Satellites by D. G. King-Hcle, which gives full details of this 
valuable and interesting work. 


Appendix XI 


The following information is based on work by E. A. 
Whitaker, formerly Director of the Lunar Section of the British 
Astronomical Association, and given in the Sectional journal, 
The Moon (Vol. 4, No. 2, page 42; December 1955). The table 
gives the approximate diameters of the smallest craters half- 
filled with shadow, and of the narrowest black line certainly 
distinguishable. Perfect seeing conditions and first-class optical 
equipment are assumed. 

Aptttute of O.G. in ins. 

Smallest crater 

Jfarrotmst Cleft 


9 miles 


5 mile 




25 » 





16 „ 














1 10 























500 yards 



The smallest craterlet that I personally have recorded is 
probably that on the summit of a mountain peak near the 
crater Beer. The instrument used was the Meudon 33-inch, 
and the diameter of the summit depression cannot have been 
much more than 500 yards. 


Appendix XII 


Thes£ outline maps have been constructed from two 
photographs. The whole lunar surface is covered, but the 
method has two disadvantages. First, the formations near the 
eastern and western limbs are under high light, and are con- 
sequently not well seen. Petavius, for instance, in the south- 
east, is really a majestic crater 100 miles across, and when 
anywhere near the terminator it is a magnificent object, but 
under this lighting it is hard to make out at aU. Secondly, the 
photographs were taken when the Moon was at favourable 
libration for the east, so that the eastern limb regions are shown 
slightly better than the western. (Note that "east" and "west" 
are used in the astronautical sense, as described in Chapter 6, 
since the IAU has now ratified the change.) 

These defects would be serious for a detailed map, but are 
not important for the present purpose. The observer may 
compare the map with the photograph given on the opposite 
page, and it will be easy to recognize the various formations. 
Once this has been done, serious work can be commenced; 
after a while, the observer will be able to identify the craters 
at a glance. 

Only a few features are named on these charts ; the remaining 
names will be found on more detailed maps. 

The notes given here are, of course, extremely brief; they 
refer only to objects which are useful for "landmark" purposes, 
and to one or two features of particular interest, such as Linne, 
the Alpine Valley and the Straight Wall. 

Names of the Lunar "Seas" 






I Heraclltui 


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v Caih»rln» ~ 

^ Q Alminon QVogel 

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b0B3Ss5fi»"O % «>slJ-"V 

J,p "" O Hlppirthiti 

~ Del,mbre ©Rbstfcu, 

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kGemlnui (ODaniell 

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<c£ f 




' Sheepsh.nki T A "V» 

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XV. TV Xf/niii: Eastern Half. The various formations may be identified on <he key map opposite. 




****-J Sehelner Bull 
S™ 5 ^ Longomontinui 


Q Herichel 
Hlppirehui"™' o^laimde 

Flammirlon* 1 *., 


r JjffiJjJEt' 

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^ MMtM ^^ 






(i) Nortk-Eastern Quadrant 

In this quadrant lie three major seas, the Maria Seren- 
itatis, Tranquillitatis and Crisium, with parts of the Mare 
Vaporum and the Mare Frigoris, as well as the northern part 
of the Mare Fcecunditatis. Mare Serenitatis is the most con- 
spicuous, and is one of the best-defined of the lunar seas. On its 
surface are only two objects of importance, the 1 2-mile bright 
crater Bessel and the famous (or infamous) Linn£, which used 
to be described as a deep crater, but is now seen in small 
telescopes as a mere white spot. A number of ridges cross the 
Mare Serenitatis. Mare Tranquillitatis is lighter in hue; 
between it and Serenitatis there is a strait upon which lies the 
magnificent 30-mile crater Plinius, which has two interior 
craterlets near its centre. 

Of the mountain ranges, the most important are those 
bordering the Mare Serenitatis : the Hsemus and the Caucasus 
Mountains, with peaks rising to 8,000 and 12,000 feet respect- 
ively. Fart of the Alps can also be seen, cut through by the 
strange Alpine Valley. This is an interesting formation, by far 



the most conspicuous of its type. South of the Haemus, and 
north of the large crater Hipparchus, can be seen the two 
important clefts of the Mare Vaporum: that of Hyginus (which 
is basically a crater-chain) and Ariadaeus. Each can be seen 
with any small telescope when near the terminator. 

Close to the eastern limb can be seen two very foreshortened 
seas, the Maria Smythii and Marginis, while the Mare Hum- 
boldtianum lies further north. These can only be well seen 
under favourable libradon. 

arago. Diameter 18 miles. It lies on the Mare Tranquillitatis, 
and has a low central elevation. Near it are several of the 
interesting swellings or "domes". 

archytas. A bright 21 -mile crater on the north coast of the 
Mare Frigoris. It has a central peak. 

aristillus. Diameter 35 miles, with walls rising to 11,000 feet 
above the floor. The walls are bright, and there is a central 
peak. Inside Aristillus are dark patches and streaks, formerly 
attributed to vegetation, though this theory is now dis- 
counted. It and Autolycus form a pair. Though it lies on the 
N.W. Quadrant, Aristillus is better shown in the next 

aristoteles. A prominent crater 52 miles in diameter. It and 
Eudoxus form a notable pair. 

atlas. Forms a pair with Hercules; it Ues N. of the Mare 
Serenitatis. Diameter 55 miles. The walls are much terraced, 
rising to 11,000 feet. There is much detail on the floor. 

autolycus. The companion to Aristillus. Autolycus is 24 miles 
in diameter, and 9,000 feet deep. It too is better shown on the 
next photograph. 

boscovttch. On the Mare Vaporum. It is a low-walled, 
irregular formation, recognizable (like its companion 
Julius Caesar) by its very dark floor. 

burg. A 28-mile crater between Atlas and Aristoteles, with a 
large central peak on which is a summit craterlet. West of 
it lies an old plain traversed by numerous clefts. 



cassini. On the fringe of the Alps, A curious broken formation, 
shallow, and 36 miles in diameter. It contains a prominent 
craterlet, A. 

clbomedes. A 78-mile crater near the Mare Crisium. It is 
broken in the W. by a smaller but very deep crater, Tralles, 

dionysius. A brilliant small crater near Sabine and Ritter. 

ENDYMJON. This 78-mile crater can always be recognized by the 
darkness of its floor. Patches on the interior seem to vary in 
hue, and should be watched. 

eudoxus. The companion to Aristoteles. It is 40 miles in 
diameter, and 1 1,000 feet deep. 

firminicus. Closely S. of the Mare Crisium. It has a diameter 
of 35 miles, and can easily be identified by its dark floor. 

gauss. A magnificent 100- mile crater, not well shown in the 
photograph, but very conspicuous when on the terminator. 

gemtnus. Diameter 55 miles. It lies near Cleomedes, and has 
lofty walls, which are deeply terraced. 

godin. Diameter 27 miles. It lies near Ariadaeus and Hyginus. 
Closely north of it lies Agrippa, which is slightly larger but 
somewhat less deep. 

hercules. The companion of Atlas. It is 45 miles in diameter ; 
the waUs are much terraced, and appear brilliant at times. 
Inside Hercules lies a large craterlet, A. 

julius 0£sar. A low-walled formation in the Mare Vaporum 
area. Owing to its dark floor, it is easy to recognize at any 

magrobius. A 42-mile crater near the Mare Crisium, with walls 
rising to 13,000 feet. There is a low compound central 
mountain mass. 

maniuus. A 25-mile crater on the Mare Vaporum, notable 
because of its brilliant walls. 

MENELAUS. Another brilliant crater; 20 miles in diameter, 
lying in the Heemus Mountains. Like Manilius, its bright- 
ness makes it easy to identify. 




posidonius. A 62-mile plain on the border of the Mare Seren- 
itatis. Adjoining it to the east is a smaller, squarish formation, 
Chacornac, and south is Le Monnier, one of the "bays" with a 
broken down seaward wall. 

proclus. Closely W. of the Mare Crisium. It is one of the most 
brilliant formations on the Moon, and is the centre of a ray 
system. Diameter 18 miles. 

sABrNE and ritter. Two 18-mile craters on die W. border of the 
Mare Tranquillitatis. N.E. of Ritter are two small equal 
craterlets. This area was photographed in detail by the U.S. 
probe Ranger VIII in 1965, and were again photographed 
from Apollo XI in 1969. The first lunar landing was made in 
the Mare Tranquillitatis, some distance east of Sabine and 

scoresby. A very distinct formation 36 miles across, near the 
North Pole. It is much the most conspicuous formation in its 
area, and is thus very useful as a landmark. 

tarunttus. A 38-mile crater S. of the Mare Crisium, with 
narrow walls and a low central bill. It is a "concentric 
crater", since it contains a complete inner ring. 

(2) South-East Quadrant 

This quadrant is occupied largely by rugged uplands, and 
large and small craters abound. The only major seas are the 
small, well-marked Mare Nectaris and most of the larger 
Mare Fcecunditatis; the Mare Australe, near the limb, is much 
less well-defined. The only mountain summits of note are 
those very near the limb, some of which attain great altitudes. 
The so-called Altai Mountains are really in the nature of a 
scarp associated with the Mare Nectaris system. 

albategnius. A magnificent walled plain near the centre of the 
disk; the companion of Hipparchus. Diameter 80 miles. The 
S. W. wall is disturbed by a deep 20-mile crater, Klein. 

capella. A 30-mile crater near Theophilus. It has a very 
massive central mountain, topped by a summit craterlet; the 
floor of Capella is crossed by a deep valley. It has a shallower 
companion, Isidorus. 



cuvier. This forms an interesting group with Licetus and the 
irregular Heraclitus. Cuvier is 50 miles across, and lies on 
the terminator in the photograph, not far from the top of the 

FABRicius. A 55-mile crater, not well shown in the photograph 
owing to the high light. It has a companion of similar size, 
Metius. Fabricius interrupts the vast ruined plain Janssen. 

gutenberg. This and its companion Goclenius lie on the 
highland between the Maria Nectaris and Fcecunditatis. To 
the north lie some delicate clefts, 

hipparchus. Well shown on the photograph, but it is low- 
walled and broken, so that it becomes obscure when away 
from the terminator. It is 84 miles in diameter, and is the 
companion of Albategnius. Ptolemaeus lies closely west of it. 

langrenus. An 85-mile crater, with high walls and central 
mountain. It is a member of the great Eastern Chain, which 
extends from Furnerius in the south and includes Petavius, 
Vendelinus, Mare Crisium, Cleomedes, Geminus and 

maurolycus. A deep 75-mile crater, well shown in the photo- 
graph; in the far south of the Moon. West of it lies the larger 
plain Stofler, which has a darkish floor. 

messier. This curious little crater lies on the Mare Fcecundit- 
atis. It and its companion, Pickering, show curious apparent 
changes in form and size. Extending W. of them is a strange 
bright ray, rather like a comet's tail. 

petavius. Not well shown on the photograph ; but it is a magni- 
ficent object when better placed. Closely E. of it is Palitzsch, 
which is generally described as a valley-like groove; but 
using very large telescopes, I have found it to be a crater- 
chain. This was confirmed by Orbiter photographs. 

piccolqmtni. A 56-mile crater S. of Fracastorius and the Mare 
Nectaris. It is deep and conspicuous, and lies at the E. end 
of the Altai range. 

rheita. A 42-mile crater. Associated with it is the famous 
Rheita Valley. This has been described as a "groove" and 
attributed to a falling meteor ; but it is in fact a crater-chain, 
and so no such explanation can be admitted. There is 



the lunar maps 

another similar formation not far off, associated with the 
crater Reichenbach. Rheita lies not far from the Marc 

stemheil. This 4.2-mile crater forms a pair of "Siamese twins" 
with its similar but shallower neighbour Watt. Near the 
Mare Australe. 

theophilus. The northern member of the grand chain of which 
Cyrillus and Catharina are the other members, Theophilus is 
65 miles across and 18,000 feet deep; it is one of the most 
magnificent of the lunar craters. There is a lofty, complex 
central elevation. 

vendelinus. One of the Eastern Chain. It is 100 miles across, 
but is comparatively low-walled, and is conspicuous only 
when near the terminator. 

vlago_. One of a group of large ring-plains near Janssen, not 
far from the Mare Australe. It is 56 miles in diameter, and 
10,000 feet deep. 

werner. A 45-mile crater, shadow-filled in the photograph. It 
forms a pair with its neighbour Aliacensis, and close by are 
three more pairs of formations: Apian- Playfair, Azophi- 
Abenezra, and Abulfeda-Almanon. 

wilhelm Humboldt, Not recognizable on the photograph, as it 
lies on the eastern limb near Petavius, but it is 120 miles 
across, with high walls and central mountain, and is magni- 
ficent just after Full Moon. 

(1) North-West Quadrant 

This Quadrant consists largely of "sea" ; there is the magni- 
ficent Mare Imbrium, with a diameter of 700 miles, as well as 
parts of the even vaster but less well-defined Oceanus Procel- 
larum, and most of the Mare Frigoris and the Sinus Roris. 
The chief mountains are the Apennines (certainly the most 
spectacular on the Moon) and the Jura Mountains, which 
form part of the Imbrian border. On the limb are the Hercynian 
Mountains. There are also the lower Carpathians, near 
Copernicus. Near Full, the most conspicuous objects are 



Copernicus and Kepler, which are the centres of bright ray 
systemsj and Plato, whose floor is so dark that it can never be 
mistaken, while Aristarchus is the most brilliant formation on 
the Moon. Eratosthenes, too, is a grand crater. 

anaxagoras, A 32-mile crater not far from the North Pole. 
It is the centre of a ray system, and is always distinct. 

archimedes. A 50-mile plain on the Mare Imbrium, with a 
darkish floor and rather low walls. It forms a superb group 
with Aristillus and Autolycus. 

aristarchus. The brightest formation on the Moon. Associated 
with its companion, Herodotus, is a great winding valley. 
This whole area is particularly subject to T.L.P.s, and should 
be systematically watched. 

copernicus. The great 56-mile ray-crater, described in the text. 

smus iridum. A glorious bay on the border of the Mare Im- 
brium. When the Sun is rising over it, the rays catch the 
bordering Jura Mountains, and the bay seems to stand out 
into the darkness like a handle of glittering jewels. 

kepler. A 22-mile crater on the Oceanus Procellarum, centre 
of a very conspicuous system of bright rays. South of it is a 
crater of similar size, Encke, which is however shallower and 

is not associated with any bright rays. 

olbers, A crater on the west limb. It lies N. of Grimaldi, and 
is 40 miles in diameter. It is not identifiable on the photo- 
graph, because of the high light and unfavourable libration; 
but it is prominent when well placed, and is the centre of a 
ray system, 

philolaus. A crater near the limb, 46 miles in diameter. It 

forms a pair with its neighbour Anaximenes. Reddish hues 
have been reported inside Philolaus, perhaps indicating 
some unusual surface deposit rather than T.L.P.S. 

Pico. A splendid 8,000-foot mountain on the Mare Imbrium, 
S. of Plato, with at least three peaks. Some way S.E. of it is 
Piton, which is also shown on the first photograph, and has a 
summit craterlet. 


the lunar maps 

PLATO. This regular, 60-mile formation has a dark floor, and is 
one of the most interesting features on the Moon, Inside it are 
some delicate craterlets which show baffling changes in 
visibility. Plato is always identifiable, and will well repay 
close and continuous attention. 

Pythagoras. A very deep crater 85 miles in diameter, not well 
shown in the photograph, but magnificent when well 
placed. There are numerous large formations in this area, 
but the whole region is very foreshortened as seen from Earth. 

straight range. A peculiar range of peaks on the Mare 
Imbrium, near Plato. It is 40 miles long, and the highest 
mountains attain 6,000 feet. 

ttmocharis. A 23-mile crater on the Mare Imbrium, containing 
a central craterlet. It is the centre of a rather inconspicuous 
system of rays. 

(2) Soutk-West Quadrant 

This Quadrant is crammed with interesting features. In the 
northern part ofit lie the well-marked Mare Humorum, part of 
the Oceanus Procellarum, and most of the vast Mare Nubium; 
the southern part is mainly rough upland. The chief mountain 
ranges are the curious low Riphajans,on the Mare Nuhiumj the 
Percy Mountains, forming part of the border of the Mare 
Humorum ; and the Dorfels, Rook Mountains, Cordilleras and 
D'Alemberts, on the limb. It is now known that these ranges are 
associated with the Mare Orientale, which is never well seen 
from Earth; Orbiter and Apollo pictures show it to be a vast, 
complex structure, unlike anything else on the Moon. 

alphonsus. The great crater close to Ptolemaeus. Dark patches 
may be seen on its floor. It was in Alphonsus that Kozyrev, 
in 1958, reported a visible outbreak of activity. The U.S. 
vehicle Ranger IX landed in Alphonsus in 1965. 

bailly. Very obscure on the photograph; but it is almost 180 
miles across, and on the Earth- turned hemisphere is thus the 
largest of the objects generally classed as "craters". It has 
been aptly described as "a field of ruins". 



billy. A 30-mile crater S. of Grimaldi. It can be identified at 
any time because of its very dark floor; it is always distinct. 
It has a near neighbour, Hansteen, with a much lighter 

birt. A crater 1 1 miles in diameter, in the Mare Nubium, near 
the Straight Wall, It has walls that rise unusually high 
above the outer plain, and inside it are two of the strange 
radial bands. 

BULLIALDUS. A splendid 39-mile crater on the Mare Nubium, 
with terraced walls and a central peak. This is one of the 
most perfect of the ring-plains. 

clavius. Clavius is 145 miles across, with walls containing peaks 
17,000 feet above the floor. Inside it can be seen a chain of 
craters, decreasing in size from east to west. When right on 
the terminator, Clavius can be identified with the naked eye. 

cruger, A low-walled crater near Grimaldi, 30 miles in 
diameter. It can be Identified on the photograph by the 
darkness of its floor, which is rather similar to Billy's. 

doppelmayer. An interesting 40-mile bay on the Mare Hu- 
morum. The seaward wall can just be traced, and there is a 
much reduced central mountain. 

eucudes. Only 7 miles in diameter, but surrounded by a 
prominent bright nimbus, well shown on the photographs. 
It lies near the Riphzean Mountains. 

fra mauro. One of a group of damaged ring-plains on the Mare 
Nubium. The other members of the group are Parry, 
Bonpland and Guericke. The unlucky Apollo 13 astronauts 
were scheduled to land in this area, subsequentiy assigned to 
Apollo 14. 

gassendi. A magnificent walled plain on the N. border of the 
Mare Humorum. It is 55 miles in diameter, and the floor 
contains a central mountain and numerous delicate clefts. 
Reddish patches have been seen in and near Gassendi, and 
are described in the text. 

mppALUs. Another bay on the Mare Humorum, not unlike 
Doppelmayer. Near it arc numerous prominent clefts, well 



seen in a small telescope, and there are also clefts on the 
floor. Near Hippalus is a small crater Agatharchides A, in 
in which I discovered two radial bands. These bands are 
useful test objects. I have seen them clearly with an aperture 
of 6 inches, but keener-eyed observers should detect them 
with smaller instruments, 

grimaldi. Identifiable at aU times because of its floor, which 
is the darkest spot on the Moon. It lies close to the west limb. 
Patches on the floor show interesting variations in hue, and 
should be watched. Grimaldi has low walls, and is 120 miles 
in diameter. Near by is a smaller formation, Riccioli, 80 
miles in diameter; it too has a very dark patch inside it. 

letronne. A bay 70 miles in diameter, lying on the shore of the 
Oceanus Procellarum not far from Gassendi. There is the 
wreck of a central elevation, 

maginus. A vast walled plain near Clavius and Tycho. It is 
very prominent when near the terminator, as in the photo- 
graph; but it becomes very obscure near Full Moon. 

mercator. This and Campanus form a conspicuous pair of 
craters E. of the Mare Humorum. Each is about 28 miles 
in diameter, and the only obvious difference between them is 
that Mercator has a darker floor. 

mersenius. A convex-floored 45-mile crater near Gassendi, 
associated with an interesting system of clefts. 

moretus. Not well shown on the photograph, but it is a splendid 
crater 75 miles in diameter and 15,000 feet deep. The central 
mountain is the highest of its type on the Moon. 

pitatus. Described by Wilkins as being like "a lagoon". It lies 
on the S. border of the Mare Nubium, and has a dark floor 
and a low mountain near its centre. It is 50 miles in diameter. 
West of it is a smaller formation, Hesiodus, and from Hcsiodus 
a prominent cleft runs towards Mercator and Campanus. 

ptolemjeus. Over 90 miles across; one of the most interesting 
formations on the Moon. It lies near the centre of the disk. 
Its floor is moderately dark. It b the northern member of a 
chain of three great craters, the other two being Alphonsus 
and Arzachel. South of this chain lies another, made up of the 
three formations Purbach, Regiomontanus and Walter. 



schickard, A formation 134 miles in diameter. It can be 
identified on the photograph, near the S.W. limb, because 
parts of its floor are darkish. Obscurations have been reported 
inside it, and it is well worth watching. 

smsAos. This and its "Siamese twin", A, lie near the dark- 
floored Criiger, not far from Grimaldi, Unfortunately they 
are not identifiable on the photograph. Sirsalis is associated 
with one of the most prominent clefts on the Moon. 

straight wall. The celebrated fault in the Mare Nubium, 
near Birt. It is shown in the photograph as a white line, but 
casts considerable shadow before Full, when the illumination 
is from the reverse direction, so that it then appears as a dark 
line. Near it are numerous craterlets, some of them visible 
with very modest apertures. The Wall lies inside a large and 
obscure ring, 

thebit. A 37-mile crater near the Straight Wall. It is inter- 
rupted by a smaller crater, which is in turn interrupted by a 
third. The group makes a useful test object for small aper- 

tycho. The great ray-crater, described in the text. 

vitello. A 30-mile crater on the border of the Mare Humorum, 
with an inner but not quite concentric ring. 

WARGENrm. Most unfortunately, this is not identifiable on the 
photograph. It lies near Schickard, and is a 55-mile plateau, 
much the largest formation of its type on the Moon. Little 
detail can be seen in small telescopes ; it is nevertheless worth 
observing. Near Wargentin is an interesting group of craters 
of which Phocylides is the largest member. 

23 8 

Appendix XIII 



Sidereal Period 

vuuawe jrom Jim, 
astronomical units 

Perihelion Aphelion 


3 3 

















1 -a 
























1 '9 

5 4 















3 4 

4 5 



1 -a 



8 4 

















5 '5 
























1 -a 











Appendix XIV 


This list includes only a few of the many annual showers. 
The dates given for the beginnings and ends of the showers are 
only approximate. 


Beginning End 

Nafad-eye Star 
mar radiant 


ftUADRANTiDS Jan. 3 Jan. 5 Beta Bootis Usually a sharp 

maximum, Jan. 

lymds Apr. 19 Apr. 22 Nu Herculis Moderate shower. 

Swift meteors, 
eta aouarids May 1 May 8 Eta Aquarii Long paths; very 

delta July 15 Aug. 10 Delta Aquarii Moderate shower. 


perseids July 27 Aug. 17 Eta Persei A rich shower. 

Meteors very 
Oct. 15 Oct 25 Nu Orionis Moderate shower. 

Swift meteors. 
Nov. 14 Nov. 17 Zeta Leorris Not usually a rich 

shower. Very 
swift meteors. 
andromedids Nov. 26 Dec. 4 Gamma Very slow met- 

Andromedae eors. Very weak 
GEMNms Dec, 9 Dec. 13 Castor Very rich shower. 

URsms Dec. 20 Dec. 22 Kocab Rather weak. 



Appendix XV 


In the following list, an asterisk indicates that the con- 
stellation was listed by Ptolemy; X, that much or all of the 
constellation is invisible in England, Zodiacal constellations 
arc distinguished by the letter Z. 



English Name 


in mag. 
Star or Stars 





The Air-Pump 



The Bird of Paradise 



The Water-Bearer 



The Eagle 




The Altar 



The Ram 



The Charioteer 




The Herdsman 




The Sculptor's Tools 



The Camelopard 



The Crab 


Canes Venatici 

The Hunting Dogs 


Cams Major 

The Great Dog 



Cards Minor 

The Litde Dog 




The Sea-Goat 



The Keel 







The Centaur 


Alpha Centauri, 






The Whale 



The Chameleon 



The Compasses 



The Dove 






English Narru Rrmarks 

lit mag. 
Star or Stan 

Coma Berenices Berenice's Hair 

Corona Australis The Southern Crown 

Corona Borealis The Northern Crown 

Corvus The Crow 

Crater The Cup 

Crux Australis 

The Southern Cross 


Aerux, Beta 


The Swan 




The Dolphin 



The Swordfish 



The Dragon 



The Little Horse 



The River Eridanus 


Achernar (Xj 


The Furnace 



The Twins 




The Crane 






The Clock 



The Sea-Scrpent 



The Water-Snake 



The Indian 



The Lizard 



The Lion 



Leo Minor 

The Little Lion 



The Hare 



The Scales 



The Wolf 



The Lynx 



The Harp 




The Table 



The Microscope 



The Unicorn 


Musca Australis 

The Southern Fly 



The Rule 



The Octant 



The Serpent-Bearer 





Rigel, Betelgeux 


The Peacock 





English Name 


lit mat- 
Star tr Stars 


The Flying Horse 






The Phoenix 



The Painter 



The Fishes 


Piscis Austrinus 

The Southern Fish 




The Poop 



The Compass 



The Net 



The Arrow 



The Archer 



The Scorpion 


An tares 


The Sculptor 



The Shield 



The Serpent 



The Sextant 



The Bull 




The Telescope 



The Triangle 



Austral e 

The Southern Triangle 

1 X 


The Toucan 


Ursa Major 

The Great Bear 


Ursa Minor 

The Little Bear 



The Sails 



The Virgin 




The Flying-Fish 



The Fox 


Some of the original names have been abbreviated; for 
instance, "Reticulum Rhomboidalis" (the Rhomboidal Net) is 
simply "Reticulum". A few constellations have alternative 
names; Scorpio is called "Scorpius" hi the list published by 
the International Astronomical Union, while Ophiuchus may 
be called "Serpentarius". 



Constellation Greek Letter /fame 

Appendix XVI 


Some of the stars have been given proper names. Most of 

these have now fallen into disuse, but since they are still 

produced occasionally the observer may find it useful to have 

a list. The names listed here are by no means all that have been 

given, but includes the more important examples. 

A few stars have more than one name (Eta Ursae Majoris 

can be "Benetnasch" as well as "Alkaid"), and some names 

can be spelled in more than one way (Betelgeux can be 

"Betelgeuse" or "Betelgeuze") . It is clearly pointless to give all 

these variations. 


Greek Letter 

































Argo Navia 




Koo She 


Suhail Hadar 



Argo Navis 




Al SuhaU Al Wazn 










































AseUus Borealis 


Asellus Australis 



Canes Venatici 


Cor Carol! 



Schj 152 

La Superba 

Cards Major 















Canis Minor 





Capri cornus 


Al Giedi 






Deneb al Giedi 
















Constellation Gnik Letter Nome 







Coma Berenices 
Corona Borealis 



Crux Australis 








Al Rijil* or Tollman 


















Al ka ffa lj idhina 


Baten Kaitos 


Deneb Kaitos Shemali 


























































* The proper name for Alpha Centauri is not generally used, except by naviga- 
tors, who refer to it as "Rigel Kent". 

| As in the case of Alpha Centauri, the proper name For Beta Crucis seems to be 
regarded as "unofficial", and is not generally used. 


Greek Letter 



























































Al Dhanab 


























Asad Australis 









Consultation Greek litter Mom 


Leo Minor 





















Z ub enelchemali 








Ke Kouan 










Al Athfar 






Yed Prior 


Yed Post 



















































Greek Litter 

















Piscis Austral is 











Kaus Meridionalis 


Kaus Australis 




Kaus Borealis 







An tares 




(= Sigma 




















Jabhat al Akrab 












Hyadum Primus 






















Greek Utter 





Triangulum Australe 



Ursa Major 


















Tania Borcalis 


Tania Australis 


Alula Borcalis 


Alula Austral is 




Ta Tsun 





Ursa Minor 






Pherkad Major 























Appendix XVII 


These are the stars generally regarded as being of the first 
magnitude. Where the star is a binary system, as with Alpha 
Centauri, the actual naked-eye magnitude is given, with the 
spectrum and luminosity of the brighter component. The three 
apparently brightest single stare are, therefore, Sirius, Ganopus 
and Arcturus. The values for the apparent magnitudes are 
based on the most recent determinations, and differ in some 
cases from those previously adopted; in earlier books, for 
instance, Arcturus was given as +0-24 instead of — 006. The 
distances and luminosities of the distant stars are rather 
uncertain: the values given here are the most recent available. 


Proper namt Mag. Sptttrum 

Dist. in Luminosity 
Light-yrs. Sun = I 

Alpha Canis Majoris 
Alpha Argas 

Alpha Centauri 
Alpha Botitis 
Alpha Lyra; 
Alpha AurigK 
Beta Ononis 
Alpha Canis Minoris 
Alpha Eridani 
Alpha Ononis 
Beta Centauri 
Alpha Aquilae 
Alpha Tauri 
Alpha Crucij 
Alpha Scorpionis 
Alpha Virginii 
Alpha Piscis Austral is 
Beta Geminorum 
Alpha Cygni 
Beta Crucii 
Alpha Lconis 










An tares 









— 0-06 







1 16 













K 5 




















80,000 ? 















25 » 

Appendix XVIII 


It may be helpful to learn the magnitudes of a few standard 
stars for each magnitude, and the following are suitable. The 
first- magnitude stars are listed separately, from Sirius ( — i -44) 
to Regulus (+ 1 -36), though Regulus is, of course, nearer il 
than 1. 


4gg*J Star 





Rho Ursae Majoris 

Eta Ursae Minoris 
Delta Trianguli 
Zeta Canis Minoris 

Theta Ursae Minoris 
Rho Corona; Borealis 
Epsilon Trianguli 

4 '99 





i£ Epsilon Canis Majoris 

Alpha Geminorum (Castor) 
Lambda Scorpii 
Gamma Orionis 

3 Alpha Arietis 

Beta Ursae Minoris (Kocab) 

Kappa Orionis 

Alpha Andromeda: (Alpheratz) 

a£ Gamma Ursa- Majoris (Phad) 

Epsilon Cygni 
Alpha Pegasi 
Delta Leonis 

3 Zeta Aquilae 
Gamma Bootis 
Delta Draconis 
Zeta Tauri 

3i Alpha Trianguli 

Zeta Leonis 
Beta Bootis 
Epsilon Tauri 

4 Beta Aquilse 

Gamma Corona: Borealis 
Delta Ceti 
Delta Cancri 

4J Nu Andromeda; 

Delta Ursa: Minoris 

Nu Cephei 

Psi Ursae Majoris 



1 '64 







3 45 








Apfyendix XIX 


v Nu 

I xi 

o Onucron 

7T Pi 

p Rho 

tr Sigma 

r Tau 

v Upsilon 

<f> Phi 

X Chi 

$ Psi 

w Omega 

























Appendix XX 







Typical Star 



36,000 + 

Greenish white 

Gamma V t-loruir 

1, Wolf-Rayet. Many 
bright lines; helium 


36,000 + 

Greenish white 

Zeta Puppis, 

Wolf-Rayet, Helium 




Spies, Bt 

Helium prominent 



Sinus, A 1 

Hydrogen lines 

G (giant) 




Beta Cassiopeia:, 

Epsilon Leotw, 

Calcium lines 

Metallic lines very 

G (dwarf) 



Sun, Ga 


K (giant) 
H (dwarf) 




Arcturus, Ka 

Epsilon Eridani, - 

Hydrocarbon bands 

M (giant) 
M (dwarf) 



Betelgeux, Ma 
Wolf 359, M6 • 


Broad titanium 
oxide and calcium 
bands or (lutings 




U Cygni 

Carbon bands 




S Ccphei, Ne 

Carbon bands. Red- 
dest of all stars 




R Andromeda: 

Some zirconium 
oxide bands. Mostly 


leparate Q., 

is reserved for nov 



Appendix XXI 


It is extremely difficult to give definite value for limit- 
ing magnitudes and separations, since so much must depend 
upon individual observers. The following table must be 
regarded as approximate only. The third column refers to 
stars of equal brilliancy and of about the sixth magnitude. 
Where the components are unequal, the double will naturally 
be a more difficult object, particularly if one star ia much 
brighter than the other. 

Apertun qf 
O.G. in incfus 

Fainttsl magnitudt 

SmalUst separation, 





1 1-4 












I3 - * 















Appendix XXII 


Appendix XXIII 

It may be useful to give the angular distances between some 
selected stars, as this will be of use to those who are not used to 
angular measurement. The distance all round the horizon is 
of course 360 degrees, and from the zenith to the horizon 90 
degrees ; the Sun and Moon have angular diameters of about 
0-5 degrees, which is the same as that of an old halfpenny 
(1 inch) held at a distance of 9 J feet from the eye. 



60 Polaris to Pollux: Alpha Ursae Majoris to Beta Cassiopeia. 

50 Sirius to Castor: Polaris to Vega 

45 Polaris to Deneb : Spiea to Antares 

40 Capella to Betelgeux: Castor to Regulus 

35 Vega to Altair: Capella to Pollux 

30 Polaris to Beta Cassiopeiae: Aldebaran to Capella 

25 Sirius to Procyon : Vega to Deneb 

ao Betelgeux to Rigel : Procyon to Pollux 

15 Alpha Andromedae to Beta Andromedae: Alpha Centauri to 


10 Betelgeux to Delta Orionis: Acrux to Agena 

5 Alpha Ursae Majoris to Beta Ursae Majoris 

4^ Castor to Pollux : Alpha Centauri to Agena 

3 Beta Scorpionis to Delta Scorpionis 

2^ Altair to Beta Aquilae 

2 Altair to Gamma Aquilae: Beta Lyrae to Gamma Lyras 

1 ^ Beta Arietis to Gamma Arietis 

I Atlas to Electra (Pleiades) 

To find the diameter of a telescopic field, select some star 
very near the celestial equator (such as Delta Orionis or Zeta 
Virginis) and allow it to drift through the field. This time in 
minutes and seconds, multiplied by 15, will give the angular 
diameter of the field in minutes and seconds of arc. For instance, 
if Delta Orionis takes 1 minute 3 seconds to pass, through the 
field, the diameter is 1 minute 3 seconds X 15, or 15' 45* of arc. 



The following list is only approximate, since again so 
much depends upon the observer as well as upon the precise 
conditions j but it may be useful as a rough guide. 


of O.G., 




sees, of are 

Angle, dcg. 







Alpha Herculis 











Gamma Leonis 





Epsilon Bootis 







2 0, 




Theta Virginis 






Theta Auriga; 





Eta Orionis 



I- 4 


Delta Cygni 

2 % 




Iota Ursae Majoris 






Zeta Bootis 





Omega Leonis 






Lambda Cassiopeiae 





* Gamma* Andromeda: 

5 "4. 





Eta Coronae Borealis 


5 '9 



* Gamma* Andromeda is the smaller component of the easy double Gamma 


Appendix XXIV 


When estimating the brightness of a naked-eye variable, 
care must be taken to allow for atmospheric dimming. The 
closer a star is to the horizon, the more of its light will be lost. 
The following table gives the amount of dimming for various 
altitudes above the horizon. Above an altitude of 45 degrees, 
extinction can be neglected for all practical purposes. 

Altitude degrees 

Dimming in magnitude! 
























Appendix XXV 


This list includes all novas since 1572 that have become 
bright enough to be visible with the naked eye. An asterisk 
denotes that the nova was too far south to be visible in England. 

Tear JVom Maximum Mag. Discoverer 


1600 P Cygni 

1604 Ophiuchi 

1 670 Vulpeculae 

1 783 Sagittae 

1848 Ophiuchi 

1866 T Corona:! 

1876 Cygni 

1 89 1 Aurigie 

1898 Sagittarii 

1 go 1 Persei 

1 903 Geminorum 

1910 Lacertae 

1912 Geminorum 

1918 Aquilae 

1918 Monocero tis 

1920 Cygni 
1925 *RR Pietoris 

1927 Tauri 

1934 DQ_ Herculis 

1936 Aquilae 

1 936 Lacertae 

1936 Sagittarii 

1939 Monocerotis 

1942 Argus 

1950 Lacertae 

i960 Herculis 

1963 Herculis 

1967 HR Delphini 

1968 Vulpeculae 
1970 Serpentis 
r 975 Cygni 


Tycho Brahe 


















Miss Fleming 






Miss Fleming 














Schwassmann, Wachmann 

I '2 






4 '5 



Whipple, Wachmann 








Dahlgren, Peltier 









I Recurrent nova. Another outburst occurred in 1946. 


Appendix XXVI 

messier's catalogue 

Number Consultation Type Magnitude Remarks 


Messier' s famous catalogue of nebular objects includes 
most of the brightest nebulae and clusters visible in England. 
It is therefore useful to give his list, as most of the objects can be 
found by means of the star maps in Appendix XXVII and can 
be picked up by means of small telescopes. 

Number Constellation 


Magnitude Remarks 

i Taurus 

Wreck of super- 


Crab Nebula. 


Radio source 

2 Aquarius 



3 Canes Venatici 



4 Scorpio 


6 '4 

5 Serpens 



6 Scorpio 

Open cluster 


7 Scorpio 

Open cluster 


8 Sagittarius 



Lagoon Nebula 

9 Ophiuchus 



io Ophiuchus 



ii Scutum 

Open cluster 


Wild Duck Cluster 

i a Ophiuchus 



13 Hercules 



Great globular 

14 Ophiuchus 



15 Pegasus 



16 Serpens 

Nebula and em- 

bedded cluster 


17 Sagittarius 



Omega or Horse- 
shoe (Nebula) 

18 Sagittarius 

Open cluster 


19 Ophiuchus 



so Sagittarius 



Trifid Nebula 

21 Sagittarius 

Open cluster 


22 Sagittarius 



23 Sagittarius 

Open cluster 


24 Sagittarius 

Open cluster 


25 Sagittarius 

Open cluster 


26 Scutum 

Open cluster 


27 Vulpecula 



Dumbbell Nebula 

28 Sagittarius 



29 Cygnus 

Open cluster 


30 Capricomus 



31 Andromeda 

Spiral galaxy 


Great Galaxy 

32 Andromeda 

Elliptical galaxy 


Satellite of M.31 

33 Triangulum 

Spiral galaxy 


Triangulum Spiral 

34 Perseus 

Open cluster 


35 Gemini 

Open cluster 


36 Auriga 

Open cluster 


37 Auriga 

Open cluster 


38 Auriga 

Open cluster 


39 Cygnus 

Open cluster 


41 Canis Major 

Open cluster 

4 -6 

42 Orion 



Great Nebula in 

43 Orion 



Part of Orion 

44 Cancer 

Open cluster 



45 Taurus 

Open cluster 



46 Argo Navis 

Open cluster 


In Puppis 

49 Virgo 

Elliptical galaxy 


50 Monoceros 

Open cluster 


51 Canes Venatici 

Spiral galaxy 


Whirlpool Galaxy 
Radio source 

52 Cassiopeia 

Open cluster 


53 Coma Berenices 



54 Sagittarius 



55 Sagittarius 



56 Lyra 



57 Lyra 



Ring Nebula 

58 Virgo 

Spiral galaxy 


59 Virgo 

Elliptical galaxy 


60 Virgo 

Elliptical galaxy 


messier's catalogue 

Xumbtr ConiUllatum Typt Magnitude Remarks 

6 1 Virgo 

Spiral galaxy 


62 Ophiuchus 



63 Canes Venatici 

Spiral galaxy 


64 Coma Berenices 

Spiral Galaxy 


65 Leo 

Spiral galaxy 


66 Leo 

Spiral Galaxy 


67 Cancer 

Open cluster 

6* t Famous old cluster 

68 Hydra 



69 Sagittarius 



70 Sagittarius 



71 Sagitta 



72 Aquarius 



73 Aquarius 

Four faint stars 

— Not a cluster 

74 Pisces 

Spiral galaxy 

IO -2 

75 Sagittarius 



76 Perseus 



77 Cetus 

Spiral galaxy 


78 Orion 



79 Lepus 



80 Scorpio 



81 Ursa Major 

Spiral galaxy 

7-9 Radio source 

82 Ursa Major 

Irregular galaxy 


83 Hydra 

Spiral galaxy 


84 Virgo 

Spiral galaxy 


85 Coma Berenices 

Spiral galaxy 


86 Virgo 

Elliptical galaxy 


87 Virgo 

Elliptical galaxy 

9*2 Radio source 

88 Coma Berenices 

Spiral galaxy 

10 '2 

89 Virgo 

Elliptical galaxy 


go Virgo 

Spiral galaxy 


92 Hercules 



93 Argo Navis 

Open cluster 

6*0 In Ptippis 

94 Canes Venatici 

Spiral galaxy 


95 Leo 

Barred spiral 



96 Leo 

Spiral galaxy 


97 Ursa Major 


i2-o Owl Nebula 

98 Coma Berenices 

Spiral galaxy 

to- 7 

99 Coma Berenices 

Spiral galaxy 



Number Constellation Type Magnitude 


100 Coma Bernices Spiral galaxy 

101 Ursa Major Spiral galaxy 

103 Cassiopeia Open cluster 

104 Virgo Spiral galaxy 



"Sombrero Hat" 

Various forms of the Messier catalogue have been given, 
notably by Owen Gingerich (Sky and Telescope) Vol. XIII, 
p. 158 (1954)) and R. H. Garstang {B.A.A. Handbook, 1964-. 
page 63). Five additions were made, ah objects observed by 
the French astronomer Mechain, and these are often included 
in the catalogue: M. 105 (elliptical galaxy in Leo), M. 106 
(spiral galaxy in Canes Venatici), M, 107 (globular in Ophiu- 
chus), and M. 108 and 109 (spiral galaxies in Ursa Major). 

M. 40 is not identifiable; it may be simply a couple of faint 
stars, or it may have been a comet. M. 91 is also an absentee, 
and this too may have been a comet, though Gingerich suggests 
that it may be identical with M. 58. There is grave doubt about 
the identities of M. 47 and M. 48 ; it has been suggested that 
M. 47 is an open cluster in Argo Navis (Puppis) and M. 48 an 
open cluster in Hydra. M. 102 may have been identical with 
M. 101, or it may possibly have been a faint spiral galaxy in 
Draco. Finally, M, 73 consists of four faint, unconnected stars, 
and is not a true cluster or nebular object. 


Appendix XXVII 


Many periodicals and some of the national newspapers 
give regular "stars of the month" charts. These are useful, but 
in my personal opinion they are of limited help to the absolute 
beginner, since they show so many objects that confusion is 
bound to result, 

I have found that the best way to learn the various groups 
is to pick them out, one by one, by means of the two leading 
constellations of our skies, Ursa Major (the Great Bear) and 
Orion, Of these, Orion is the more brilliant, but it is not always 
visible in England, whereas the Bear never sets. 

Using these two constellations as "signposts in the sky", 
it is possible to identify the other groups, and this system is 
developed in the maps given here. The key maps, I and II, 
will enable the beginner to find his way about in Maps IV to X. 
There can be little difficulty in finding Orion and the Great 
Bear; for one thing, there will always be someone near by who 
knows them. 

The star-maps given here are not precision charts; nor are 
they intended to be, but it is hoped that they will be of some 
use as an aid to finding one's way about the sky. 

In the constellation notes, all stars down to magnitude 3*5 
have been listed under the heading "Chief Stars". All the 
doubles, variables and clusters mentioned are easy objects. 



Almost everyone must know the Great Bear. Its seven stars 
are a familiar feature of the night sky, and it is of course so far 
north that it never sets in the latitude of England. The proper 
names of the seven are frequently used : in addition, Merak and 
Dubhe are popularly known as the "Pointers". 

The first step after having identified the Bear is to find the 
Pole Star. Imagine a line drawn from Merak through Dubhe, 
and prolonged; it will reach a second-magnitude star rather 
"out on its own", and this is Polaris. The Little Bear, Ursa 
Minor, can then be picked out, bending back towards the Great 
Bear itself. The stars are much fainter, but one of them, the 
rather reddish Kocab, is of magnitude 2. 

Now imagine a line from Alioth, in the Great Bear, through 
Polaris. Prolonged for an equal distance on the far side of 
Polaris, it will reach five brightish stars (magnitudes 2 to 3) 
arranged in a rough W. This is Cassiopeia, which, like the 
Bears, never sets in England. 

A line from Megrez through Dubhe will come eventually to 
Capella, which is one of the brightest stars in the entire sky. 
It is circumpolar in England, but at its lowest, as during 
summer evenings, it almost reaches the horizon. In winter 
evenings it is high up, and may indeed pass overhead. If you 
see a really bright star straight above you, it can be only 
Capella or Vega; Capella is yellowish, and may be recognized 
by the small triangle of stars close by it, whereas Vega is 
decidedly blue. Vega can be found by means of a line beginning 
at Phad, passing between Megrez and Alioth, and prolonged 
for some distance across the sky. 

The remaining stars shown in Map I are not circumpolar. 
The Twins, Castor and Pollux, may be found by means of a 
line from Megrez through Merak; they are at their best in 
winter, Rcgulus and the other stars of the Lion, found by a line 
from Megrez through Phad, seem to follow the Twins in the 
sky; the curved arrangement of stars rather like a reversed 
question-mark, of which Regulus is the brightest, is known as 
the "Sickle of Leo", and is easy to recognize. Even easier is 
Arcturas, about as bright as Capella and Vega. This is found 
by means of a line from Mizar through Alkaid, and curved 





Ursa Major 



Leo . \f** 


\. Virgo 






rather downwards; if the curve is continued through Arcturus 
it comes to another ist-magnitude star, Spica in Virgo, 
Arcturus and Spica are prominent features of the spring and 
summer skies of England. 

It may be added that Arcturus shines with a distinctly orange 
light, so thiit it cannot be confused with Capella or Vega. 



It is a pity that Orion is not circumpolar in England, as 
it is a magnificent "signpost", as well as being a beautiful 
constellation in itself. It cannot be mistaken, as all its chief 
stars are brilliant, two of the first magnitude (Betelgeux and 
Rigel) and five of the second. Mintaka, Alnilam and Alnitak 
form the famous Belt. The periods of visibility of Orion in 
England can be judged from the following : 

January 1st Rises 4 p.m., highest 10 p.m., sets 5 a.m. 

April 1 st Rises in daylight, highest in daylight, sets 11 p.m. 

July 1st Rises 4 a.m., highest in daylight, sets in daylight. 

October 1st Rises 10 p.m., highest 5 a.m., sets in daylight. 

It must be understood that these times arc only very rough ; 
Orion covers a considerable area, and takes some time to 
"rise". It is however clear that the constellation is best seen in 
winter and in the early mornings in autumn. 

The first-magnitude stars in the key map are easy to find 
if Orion can be seen. The three stars of the Belt (Mintaka, 
Alnilam and Alnitak) point downwards to Sirius, which is the 
most brilliant star in the sky, though of course less bright than 
Venus, Jupiter or Mars when well placed. Upwards, the Belt 
stars indicate Aldebaran in Taurus, a reddish first-magnitude 
star of about the same colour and brightness as Betelgeux. 

Bellatrix and Betelgeux point more or less to Procyon, in 
Canis Minor, which is not much fainter than Rigel ; if this fine 
is continued and curved slighdy it reaches a reddish 2nd- 
magnitude star, Alphard in Hydra, known as "the Solitary 
One" because it lies in a very barren region. The Twins, 
Castor and Pollux, can be found by a line from Rigel through 
Betelgeux; since they can also be found by using Ursa Major, 
this links the two key maps. Capella is indicated by a line from 
Saiph through Alnitak. Diphda in Cetus, the other star shown 
in the diagram, is less easy to find. It is only of mag. 2, and is 
frequently visible when Orion is below the horizon. 

Undoubtedly a winter evening is the best time to start star 
recognition, since then both our "signposts", Orion and the 
Bear, can be seen. If a start be made in summer, we must do 
without Orion; but the Bear can by itself teach us the way 







► Algol 

/ Pleiades 



PROCYON ^" ° r 'on 










about the heavens, and even though the stars seem at first 
to be arranged in a chaotic manner it takes surprisingly 
little time to find one's way about. 

Each of the following charts contains at least one key map 
object. Exact positions of telescopic objects, in right ascension 
and declination, are not given here, because an observer who 
possesses a telescope equipped with setting circles will in any 
case need a more detailed set of charts. By far the best star 
adas for the average worker is Norton's, published by Gall and 



This is the North Polar region. The stars in it are of course 
circumpolar in England, and will quickly be recognized. 

ursa major. This has already been described at length. 
The chief stars are Epsilon (Alioth) and Alpha (Dubhe) (i-8), 
Eta (Alkaid) (1*9), Zeta (Mizar} (2*1), Beta (Merak) and 
Gamma (Phad) (2-4), Psi and Mu (3-0), Iota (3-1), Theta 
(3-2), Delta (Megrez) (3-3) and Lambda (3-4). Part of the con- 
stellation extends on to Map VI. 

Double Star. Zeta (Mizar). Naked- eye pair with Alcor. 
In a low power Mizar is itself double; mags. 2-2, 3-9; dist. 
14**5; -P*A. 150 . Between this pair and Alcor is another star. 
Nu; mags. 37, 9-7; distance y"-2: PA 147°. 

Variables. T: mag. 5-5 to 13, period 257 days. Spectrum 
Me: red. An easy object near maximum. 

R: mag. 5-9 to 13; period 302 days. Spectrum Me: red. 
like Tj an easy object near maximum. 

Clusters and Nebulx. M.81 and M.82; two galaxies, close 
together, identifiable without much difficulty. 

M.97: The Owl Nebula, a planetary so called because its 
two hot stars do give it the look of an owl's face with high 
powers. It is very faint with small apertures, but is worth 
looking for. 

ursa minor curves down over the stars of Ursa Major. 
Chief stars: Alpha (Polaris) (2-0), Beta (Kocab) (2*0), Gamma 
(3*1). Kocab is a fine orange star. 

Double Star. Polaris. Mags. 2-o, 9-0; distance 18* -3, P.A. 
2 1 7°. An easy object with aperture 3 in. or more. 

draco. A long, winding constellation, stretching from 
Lambda (between Dubhe and Polaris) as far as Gamma, which 
lies near Vega. The chief stars are Gamma (2-2), Eta (2-7), 
Beta (2-8), Delta (3-1), Zeta (3-2) and Iota (3*3). Alpha or 
Thuban (3-6) used to be the pole star in ancient times. 

Double Stars. Nu; magnitudes 4-5, 4-5; distance 62*. This 
is a very wide, easy double. 

Eta: magnitudes 2-7, 8-0 ; distance 6"; P.A. 142 . This can 
be seen with a 3-inch refractor. 





Epsilon: magnitudes 4-0, 7-5; distance 3* -3; P.A. 009 °. 

cepheus is not one of the easier constellations to identify, 
but it is useful to remember that Gamma Cephei lies more or 
less between Polaris and the W. of Cassiopeia. It is better shown 
on Map VII. Chief stars: Alpha (2*4), Beta (3*1), and Gamma 
(3-2). Telescopic objects are given in the notes on Map VII. 

CAMELOPARDtrs. A large, dull constellation, with no stars 
brighter than the 4th magnitude, and with no objects or 
particular interest. It is in fact one of the most barren regions 
of the heavens. 


The limes of rising and setting of Orion, in England, were 
given in the notes on Map II. Capella is just circumpolar, but 
can almost graze the horizon. Perseus is shown in part, and also 

Orion is probably the most glorious constellation in the 
heavens, and is easy to recognize. Betelgeux is a fine sight with 
a lower power (spectrum M; orange- red), while Rigel is 
brilliantly white. Rigel appears only very slightly less brilliant 
than Arcturus and Vega, The other leading stars are Gamma 
(BeUatrix) (1*6), Epsilon (Alnilam) (1-7), Zeta (Alnitak) 
(i-8), Kappa (Saiph) (2-1), Delta (Mintaka) (2-3, but slightly 
variable), Iota (2-8), Pi 3 (3*2), Eta (3-4) and Lambda {3-5). 

Double Stars. Rigel: magnitudes o-i, 7-0; distance g*-2; 
P.A. 206 . A test for a a-in. O.G.; easy with a 3-in, The 
companion is said to be bluish, but to me it always appears 

Eta; magnitudes 3-6, 4-8; distance 1 *'5J P.A. 083 . 

Lambda: magnitudes 3-6, 5-5; distance 4*' , 4; P.A. 043 , 

Zeta: magnitudes 1-9, 4-2; distance 2* -4; P.A. 164 . I find 
this very hard with anything less than 3-in. aperture. 

Iota: magnitudes 3-0, 7-4; distance 11 '-4; P.A. 142°. 
Immersed in nebulosity. 

Theta: the Trapezium, a multiple star. Magnitudes 6-0, 



7 -Oj 7 -o, 7 "5, All four stars are easy in a 3-in. O.G. Immersed 

in the Great Nebula, M.42. 

Sigma: another multiple. The magnitudes of the four bright- 
est stars are 4-0, 7-0, 7-5 and 9-9. Less striking than Theta, 
but well worth examination. 

Delta: magnitudes 2-3 (var.), 67; distance 53"; P. A. ooo°. 
Very wide and easy. 

Variables. Betelgeux: o-o to 1-2. This is a greater range than 
is given in most textbooks, but Sir John Herschel recorded that 
he saw it outshine Rigel, and this has also been my experience. 
The best comparison star for normal periods is of course 
Aldebaran; another, useful when Betelgeux is faint, is Pollux. 

U (not far from Zeta Tauri). Magnitudes 5-5 to 12-6. 
Period 372 days. A red, Me-type long-period variable. 

Delta (Mintaka) : an eclipsing binary of small magnitude 
range (2-20 to 2-35). 

Clusters and Nebula. M.42: the Sword of Orion, visible to 
the naked eye, and the most prominent of all galactic nebula:. 
It is a splendid sight in a small telescope; dark nebulosity 
may be seen close to the Trapezium. 

lepus is a small constellation near Orion. The chief stars 
are Alpha (2*6), Beta (2-8), Epsilon (3-2) and Mu (3.3). 

Double Stars. Kappa: magnitudes 4-95 7-5; distance 2* -6; 
P.A. 000 °. The primary is yellowish and the companion bluish. 

Beta: magnitudes 2-8, 9-4; distance 2 "-5; P.A. 313 . 

Variable. R: magnitude 5-9 to 10-5; period 432 days. This 
is an intensely red star of spectrum N. It is not hard to find when 
near maximum. 

columba lies below Lepus, and is too far south to be well 
seen in England. Chief stars: Alpha (2-6), Beta (3*1). The 
constellation contains no features of particular interest. 

caelum has no star brighter than Alpha (4-5), and is always 
very low in our latitudes. 

Double Star: Gamma; magnitudes 4*7, 8-5; distance 3*; 
P.A. 310 . 

ERiDANUS. A very long constellation, of which the chief stars 
are the first-magnitude Achernar, and Beta (2-8), Theta 
1 273 


(2-9) and Gamma (30). Achemar and Theta never rise in 
England, but are shown in Map XV. 

Double Star. Omicron 2 : magnitudes 4-0, g-o; distance 82*: 
P. A. 1 07°. Theta is double; separation 8". 

Fornax has no star brighter than Alpha (4-0). It is low in 
England, and contains no features of interest. 

cetus is another long, winding constellation; the rest of it 
is shown in Map X. Chief stars: Beta (2-0), Alpha (2-5), 
Eta and Tau (3-5). Alpha is a fine orange star. 

Double Stars. Gamma: magnitudes 3-6, 62; distance 3"; 
P.A. 295 , 

66: magnitudes 6-o, 78; distance 16 '-3; P.A. 232 . The 
primary is yellow and the companion blue. This is in a low- 
power field with Mira, and is a useful guide when Mira is 

Variable, Omicron (Mira): magnitude 17 to 9-6; period 
331 days. This interesting star is fully described in the text. 

Nebula. M.77: a fairly easy object, one degree away from 
Delta. It is actually a spiral galaxy. 

taurus. This is a Zodiacal constellation of great interest. 
Apart from Aldebaran, the chief stars are Beta (1 -6), Eta 
(Alcyone) (2-9), Zeta (3-1), and two of the Hyads, Theta 2 (3-4) 
and Epsilon (3-5). Beta Tauri is also known as Gamma Auriga. 

Double Star. Aldebaran has a 13th magnitude companion; 
distance 121 "; P.A. 034 . This is a wide optical double, but the 
faintness of the companion makes it a useful test object. 

Variable. Lambda: magnitude 3-3 to 4-2; period 3-9 days. 
Spectrum B3. This is an eclipsing binary of the Algol type. 

Clusters and NebuU. M.i: the remarkable "Grab Nebula", 
near Zeta, described in the text. 

The Pleiades and Hyades are also described in the text. The 
Hyades, which are scattered, are best seen in binoculars. 

auriga. One of the brightest of the northern groups. Capella 
is shown in both Key Maps, and is surpassed by only three 
other stars visible from England : Sirius, Vega and Arcturus. 
The difference between Vega and Capella is only i/roo of a 
magnitude. Capella is yellow, and can be identified by the 
three fainter stars (Epsilon, Zeta, Eta) close by it; these have 



been termed the "Haedi", or Kids. Gamma Auriga; is now 
known as Beta Tauri. This is one of a few cases of stars being 
included in two constellations; others are Alpha Andromedae 
(=Delta Pegasi) and Gamma Scorpionis (= Sigma Libra;). 

The other chief stars of Auriga are Beta (1*9), Iota and 
Theta (2*6) and Eta (3*2). Epsilon, the vast giant, is variable; 
it is comparable with Eta, The magnitude range is small, and 
this applies also to the other giant eclipsing binary, Zeta, 
whose fluctuations will not easily be detected without in- 

Epsilon's magnitude varies from 3-1 to about 4-4, and the 
period is just over 27 years. 

Double Star. Theta: magnitudes 2-6, 7-1; distance 2"*8; 
P.A. 333 . I always find this rather difficult with a 6-in. 
reflector; it is said to be a test for a 4-in. O.G. 


The constellations shown in this map are at their best in 
winter and spring evenings. The following times of rising and 
setting in England are for Cancer, and are of course very 
rough. Cancer is a Zodiacal constellation, as are Gemini and 

January 1st Rises 6 p.m., highest 2 a.m., set in daylight. 
April 1 st Rises in daylight, highest 8 p.m., sets 4 a.m. 
July 1st Rises in daylight, highest in daylight, sets in 

October 1st Rises at midnight, highest 8 a.m., sets in daylight. 

canis major is most notable because of the presence of Sirius, 
the brightest star in the sky. The other chief stars are Epsilon 
(1-5), Delta (i-8), Beta (2-0), Eta (2-5), and Omicron 2 and 
Zeta (3*0). The group is easy to find from Orion. Actually there 
are few interesting telescopic objects in Canis Major, but 
M.41 is a bright cluster well worth looking at. 

canis minor contains Procyon; the only other bright star is 
Beta (2 -9). 





monoceros. A large, faint constellation with no star brighter 
than the fourth magnitude; it lies in the area enclosed by 
Procyon, Sirius and Betelgeux. The Milky Way passes through 
is, and there are some rich telescopic fields, so that the region 
it worth sweeping with low powers. 

Doable Star. Beta: a triple. Magnitudes 5-0, 5-5, 5*9; dist- 
ances 7*-4 and 2"-8; P.A.S 132 and 105 . 

Cluster. Around the 6th magnitude star 12 Monocerotis is a fine 
open cluster, H.VII.2 (not in Messier's catalogue). It Ues between 
Betelgeux and the fourth-magnitude star Delta Monocerotis. 

argo navis. Nearly all of this grand constellation, including 
Canopus, is too far south to be seen in England; it is shown in 
Map XIV. A few stars of Puppis, including Rho (2-7) and Xi 
(3-3) can be made out, and a few stars of pyxis nautica can 
also be seen low down on the horizon. 

Cluster. M46: a beautiful small cluster, roughly between 
Rho Argus and Alpha Monocerotis. 

Gemini. This is one of the grandest of all constellations. As 
well as Pollux and Castor, it includes other bright stars : Gamma 
(1-9), Mu and Epsilon (3-0), Xi (3*4) and Delta {3*5). 
Moreover, the Milky Way passes through it. Castor and Pollux 
can be found from either key map. Pollux, rather orange in 
colour (type K) is now appreciably brighter than Castor, 
though it seems that in Ptolemy's day this was not the case. 
There are plenty of interesting objects in Gemini. 

Double Stars. Castor: magnitudes 1-9, 2-8; distance i-8"; 
P.A. 151 . A fine double ; binary, period 380 years. As described 
in the text, Castor is a multiple system ; Castor C, magnitude 
9-1, lies at 73". 

Delta: magnitudes 3-5, 8-2; distance 6'- 7; P.A. 210 . Test 
for a 2-in. O.G., though I always find it rather easy with such 
an aperture. 

Lambda: magnitudes 3-7, io-o; distance 10* ; P.A. 033 . 

Kappa: magnitudes 4-0, 8-5; distance 6*7; P.A. 235 . 

Variables. Eta: a long-period M-type variable; magnitude 
3 -3 to 4-2 ; official period 231 days, but I have my doubts! 

Zeta: magnitude 3*7 to 4-3; period 10-2 days. Spectrum G. 
A typical Cepheid. A useful comparison star is Nu (4*1). 

R: magnitude 6-o to 14; period 370 days. 



Cluster, M.35. A fine open cluster, a splendid sight in a small 
telescope. Mu and Eta act as excellent "guide stars" to it, 

cancer. A faint constellation, the brightest stars being Beta 
(3-8), Iota (4-1) and Delta (4-2), but it includes some interest- 
ing objects, such as Praesepe. It is not unlike a very dim and 
ghostly Orion, and lies in the area enclosed by Pollux, Procyon 
and Regulus, 

Double Stars. Zeta: magnitudes 5-0, 57; distance 1"; binary, 
period 60 years. It was at its widest in the year i960, and is 
now closing up again. There is a third component; magnitude 
6-1, distance 5"*7. 

Iota: magnitudes 4-3, 6-3; distance 31"; P. A. 30 7 . The 
larger star is yellowish, the companion bluish. 

Variable. R: magnitude 5-9 to 11-5; period 362 days. An 
M-type, long-period variable. 

Clusters. M.44 (Pnesepe). One of the best of the open clusters. 
It has been described in the text, and can be seen with the 
naked eye on any reasonably transparent moonless night. 

M.67, A conspicuous telescopic object close to Alpha (4*3). 

hydra. Apart from Argo Navis, which is now divided up, 
Hydra is the largest constellation in the sky; parts of it are also 
shown on Maps VI and IX. It is however rather barren. The 
chief stars are Alpha (2*0), Gamma (3-0), Zeta and Nu (3-1), 
Pi (3-2) and Epsilon (3-4). Alphard is shown on the Key Map 
II; it is easy to find, as it is distinctly reddish, and appears 
very isolated. Its name of "the Solitary One" suits it well. It 
can be identified by continuing the "sweep" from Bellatrix 
through Betelgeux and Procyon and, incidentally, Castor and 
Pollux point to it. It is a fine object in a low power. 

Double Stars. Theta: magnitudes 4-9, io-8; distance 38*; 
P.A. 185 . The faintness of the companion makes it a useful test. 

Epsilon: magnitudes 3-6, 7-7; distance 3"-6; P.A. 253 . 
This is in the "head" of Hydra, which is easy to find, as it lies 
roughly midway between Procyon and Regulns. The bright com- 
ponent is a close binary with a period of 1 5 years. A 1 2-mag. 
star lies at 20*. 

sextans. A faint and unremarkable constellation, with no 
star as bright as the 4th magnitude, and no interesting telescopic 



Parts of Leo and Taurus are included in this map, but are 
better shown in Maps VI and IV respectively. 


This area contains some interesting features; Regulus, 
Spica and Arcturus are shown in Key Map I. The rough times 
of rising and setting for Spica, in England, are: 

January 1st Rises 1 a.m., highest 6 a.m., sets in daylight. 
April 1st Rises 7 p.m., highest midnight, sets 5 a.m. 
July isi Rises in daylight, highest in daylight, sets 1 1 p.m. 

October 1st Rises in daylight, highest in daylight, sets in 

leo. A large, important constellation. Regulus is of course 
the chief star, and other bright stars are Gamma (2-0), Beta 
(2-1), Delta (2-6), Epsilon (3-0), Theta (3-3) and Zeta (3-5). 
The curved fine of stars beginning with Regulus is known as the 
Sickle, and is a prominent feature; the triangle formed by 
Beta, Delta and Theta is also easy to find. Beta is a secular 
variable. Ptolemy made it of the 1st magnitude, but it is now 
below the second. As it is suspected of variability, it is well 
worth watching ; Gamma makes a good comparison star. 

Double Stars. Gamma: magnitudes 2-3, 3-8; distance 4* -3; 
P.A. 121 . A fine binary, with a period of 407 years. 

Iota: magnitudes 3-9, 7-0; distance o"-6; P.A. 015 . 

Variable Star. R: magnitude 5-0 to 10-5, period 312 days. 
A long-period M-type variable, visible to the naked eye near 

leo minor. A faint group, about midway between Regulus in 
Leo and Merak in Ursa Major. It contains no star brighter than 
magnitude 4. The only object of interest is the M-type long- 
period variable R; magnitude 6-2 to 12-3, period 370 days. 

Virgo. In shape Virgo is rather like a roughly-drawn Y. The 
brightest star is of course Spica; others are Gamma (2-8), Epsilon 



(2-9) and Zeta (3-4). The "bowl" of the Y, in the area enclosed 
by it and Beta Leonis, is very rich in faint galaxies, and is well 
worth sweeping. 

Double Stars. Gamma: magnitudes 36, 37; distance about 
5*, This is a magnificent binary, with a period of 172 years, 
and one of the best of all double stars for small telescopes. 

Theta: magnitudes 4-0, 9-0; distance 7*; P.A. 343 . There is 
a loth-magnitude star at a distance of 71 *, making a useful test. 

Variables. R: magnitude 5-9 to 120; period 145 days, i'a^i 



S: magnitude 5-6 to 12-3; period 372 days. Like R, a long- 
period variable of spectrum M. 

coma Berenices and canes venatici lie in the area enclosed 
by the Great Bear, Regulus, Beta Leonis and Arcturus. Coma 
contains no star brighter than magnitude 4§, but it is a rich 
area, and to the naked eye looks almost like a very scattered 
star-cluster, so that it is worth sweeping. Canes Venatici has 
one star, Alpha, of magnitude 2-9; it is a wide optical double; 
magnitudes 3-0, 5-6, distance 20", P.A. 228 . Canes Venatici 
is so far north that it is circumpolar in England, 

There are many clusters and nebulae in these two con- 
stellations, which are shown on the map and are well worth 
looking for. 

bo6tes is shown in part, but is described with Map IX. 

hydra is also partly shown, the brightest star being Nu 
(3*1). In this part of the constellation lies the interesting red 
N-type irregular variable U Hydras, which has a magnitude 
range from 4-5 to 59. 

crater. The brightest stars in this small group are Delta 
(3-8), Gamma (4-1) and Alpha (4-2), which form a triangle 
not far from Nu Hydra. Not far from the reddish Alpha is the 
very red irregular variable R Crateris, with a magnitude range 
of from 8 to 9. 

corvus. This xs easy to find, as its four chief stars are of 
about the third magnitude (Gamma, 2-6; Beta, 2*7; Delta 
and Epsilon, each 3-0) and form a quadrilateral. To find it, 
pass a line from Arcturus midway between Spica and Gamma 
Virginis, the double star at the branch of the "Y". Delta Corvi 
is a double; magnitudes 3-1, 8-2; distance 24"; P.A. 21 2°. 



Of the groups in this map, all are circumpolar apart from 
sections of Andromeda and Triangulum. Ursa Minor and 
Camelopardus are also shown, but are described with Map III. 

Cassiopeia, shown in Key Map I, is one of the most interest- 
ing and conspicuous of the northern constellations. The Milky 
Way passes through it, and there are many rich telescopic fields. 
Of the chief stars, Alpha (Shedir) and Gamma are variable; 
the others are Beta (2-3), Delta {27) and Epsilon (3-4), which 
of course serve as excellent comparison stars. 

Double Stars. Alpha: magnitudes 2-2 (var.) and 9-0; distance 
63*; P.A. 280°, A wide optical double. 

Eta: magnitudes 3 7, 7-3; distance 11 '-2; P.A. 298 . Binary. 

Iota: a fine triple. Magnitudes 4-2, 7-1, 8-o; distances 2" % 
7*-5jP.A.S25i°, 113 . 

Variables. Gamma: magnitude 1 7 to 3*4: irregular, and now 
classed as a "pseudo-nova". A most peculiar star, with a most 
unusual spectrum. Between 1965 and 1974 its magnitude 
averaged around 2 •%. It is well worth watching. 

Alpha. This was long classed as a variable: recently doubts 
have been cast on the reality of the fluctuations, but my own 
rough observations between 1936 and the present time indicate 
that the magnitude fluctuates irregularly between 2*1 and 
2-5. Also worth watching is the irregular Rho {page 327). 

R: magnitude 5-3 to 13-0; period 432 days. Spectrum M. 

Clusters and Nebula. M.52: a fairly bright cluster. Alpha 
and Beta act as "guides" to it. 

M.103; An open cluster close to Delta. 

cepheus. This is not too easy to identify. The chief stars 
are Alpha (2-4), Beta (3-1), Gamma (3-2), Zeta (3-3) and 
Eta (3*4} . Gamma lies between Beta Cassiopeia and Polaris; 
the main part of the constellation between Cassiopeia and 
Vega. The triangle made up of Zeta, Delta and Epsilon 
is the most conspicuous feature. On the whole, Cepheus is 
rather a barren group. 

Double Stars, Beta: magnitudes 3-3, 8-o; distance 14*; P.A. 
250 . 



Kappa: magnitudes 4-0, 8-o; distance 7*-5; P.A. 122 . 

Variables. Delta: magnitude 3-5 to 4-4; period 5*37 days. 
The prototype Cepheid. 

Mu: magnitude 3-6 to 5-1 ; irregular. Sir William Herschel's 
"garnet star". It is of type M, and is probably the reddest of 
the naked-eye stars; a splendid object in a low power. 

T: magnitude 5-5 to 96; period 391 days. Spectrum M. 

AR; magnitude 7-1 to 7-8; period 116 days. Semi-regular. 

lacerta is a small constellation near Cepheus. It contains 
no star brighter than the 4th magnitude, and no objects of 
special interest. 

perseus. A grand constellation. It lies between Cassiopeia 
and Aldebaran; the chief star, Alpha (i-8) can be found by a 
line drawn from Gamma Cassiopeia: through Delta Cassiopeiae 
and prolonged. The other leading stars are Beta (Algol) 
(variable; 2-1 at maximum), Zeta (2-8), Epsilon and Gamma 
(2*9), Delta (3-0) and Rho {variable; 3*2 at maximum). The 
Milky Way is particularly rich in Perseus. 

Double Stars. Zeta: magnitudes 2*8, 9-4; distance 12 "-5; 
P.A. 208 . The chief component is a very luminous Bi-type 

Eta: magnitudes 4*0, 8-5; distance 28 "'•4: P.A. 300 °. The 
primary is yellow, the companion bluish. 

Epsilon: magnitudes 2-9, 83; distance 9"; P.A. 009 . 

Variable Stars. Beta (Algol); magnitude 2-1 to 3-3. The 
prototype eclipsing binary, fully described in the text. 

Rho: magnitude 3-2 to 4*2 ; an M4-type irregular. A suitable 
comparison star is Kappa, magnitude 4-00. 

Clusters. M.34; a fine open cluster, roughly between Kappa 
Persei and Gamma Andromedas, visible to the naked eye on a 
transparent night. 

H.VI.33 and 34. The "Sword-Handle" clusters, described 
in the text. They are visible to the naked eye, and in my view 
are the most beautiful of all open clusters. Between them is a 
faint red star. 

andromeda. This is a bright constellation, the leading stars 
being Beta (2-0), Alpha and Gamma (2-1) and Delta (3-2). 







Alpha is included in the Square of Pegasus, and is also known 
as Delta Pegasi. It can be found by means of a line drawn 
from Epsilon Cassiopeise through Delta Cassiopeia, and 

Double Stars. Gamma; magnitudes 2-2, 5*0; distance 9* -8; 
P.A. 060 . A grand double, the components being yellow and 
blue. The small star is again double; magnitudes 5-4, 6-2; 
distance o* -7; P. A. 109 , 

Variable. R: magnitude 5-9 to 15; period 410 days. A long- 
period M-type variable, too faint at minimum for small 
apertures. It lies near Theta Andromedae (4-4). 

Galaxy. M.31 ; the Great Spiral, described in the text. It is 
visible to the naked eye as a misty patch close to Nu Andro- 
meda; {4 -4), but a telescope of large size is needed to show its 

Triangulum. A fairly conspicuous little group near Andro- 
meda, the leading stars being Beta (3-0) and Alpha (3-4). 

Variable. R: magnitude 5 -8 to 12; period 266 days. Spectrum 

Galaxy. M.33. A large but rather faint and ill-defined object, 
roughly between Alpha Trianguli and Beta Andromedae, 

lynx. One of the most barren of all constellations. It adjoins 
Camelopardus, and lies between Ursa Major and the Twins 
(Castor and Pollux). There are no bright stars or interesting 
telescopic objects worthy of men don here. 





This is a very rich area, best seen in summer. Vega and 
Deneb are just circumpolar in England, and the approximate 
time of rising and setting for Altair are given below. It must be 
remembered that in all these "rising and setting" tables, 
allowance must be made for Summer Time. 

January ist Rises 6 a.m., highest in daylight, sets 8 p.m. 

April rst Rises midnight, highest 7 a.m., sets in daylight. 

July ist Rises in daylight, highest 1 a.m., sets in daylight. 

October ist Rises in daylight, highest 7 p.m., sets 2 a.m. 

Vega and Deneb are shown on the first key map. Vega is 
almost overhead at midnight near midsummer, and can be 
recognized by its brilliance and by its bluish colour, which 
differs strongly from the yellowish hue of Capella, which 
occupies the overhead position at times during the winter. 

lyra. Though Lyra is a small constellation, and Vega is the 
only star above the third magnitude, it is remarkably rich in 
telescopic and other interesting objects. After Vega, the leading 
stars are Gamma (3-2) and the eclipsing binary Beta. The 
quadrilateral made up of Beta, Gamma, Delta and Zeta is 
easily recognized. 

Double Stars. Epsilon. The famous double-double, described 
in the text. The two main components can be split with the 
naked eye; magnitudes 4-5 and 47 ; distance 208". Epsilon 1 ; 
magnitudes 4*6, 6-3 ; distance 2 **8; P. A. 00 1°. Epsilon 2 : magni- 
tudes 4-9, 5-2; distance 2 "-2; P. A. 099 . Of the two, Epsilon 1 
is the easier to divide, but both pairs are well visible in a 3-inch 

Zeta: magnitudes 4-3, 5-9; distance 44*; P. A, 150 . A wide, 
easy double. 

Eta: magnitudes 4-5, 8-o; distance 28 "; P.A. 083 . 

Vega: has a companion, magnitude 10*5, at a distance of 
56' and a P.A. of 169 . This is an optical pair, not a binary 
system. The faintness of the companion makes it a convenient 
test object. 

Variables. Beta: magnitude 3-4 to 4*4, period 12-9 days. 



Eclipsing binary, described in the text. Gamma is a good 
comparison star; others are Zeta (4-1) and Kappa (4-3). 
It may be added here that the magnitude of 4-1 for Zeta as 
seen with the naked eye is the result of the combined light of 
the 4*3 and 5-9 magnitude components. 

R: magnitude 4-0 to 5-0; a red M-type semi-regular variable. 

Nebula. M.57. Planetary. The Ring Nebula, described in the 
text. It can be seen with a small aperture, but the central star 
is extremely difficult even with large instruments. The object is 
easy to find, as it lies directly between Beta and Gamma Lyrae. 

cyqnus. The Swan, but also, and perhaps more appro- 
priately, known as the Northern Cross. It is a superb constella- 
tion, in a rich part of the Milky Way. The chief star is Deneb; 
other bright stars are Gamma (2-2), Epsilon (2-5), Delta (2-9), 
Beta (3-1) and Zeta (3*2). It is worth remembering that Beta, 
the faintest of the stars forming the Cross, lies roughly between 
Vega and Altair. 

Double Stars. Beta (Albireo): magnitudes 31, 5-1; distance 
34**6; P.A. 055°. Yellow primary, green companion. I regard 
this as the loveliest double in the sky, and it is a superb object 
in any small telescope. 

Delta: magnitudes 3-0, 6-5; distance 2"; P.A. 240 . A well- 
known test. Binary, with a period of 32 1 years. 

61: magnitudes 5-6, 6-3; distance 28*; P.A. 142 . The 
celebrated star which was the first to have its distance measured. 

Zeta: magnitudes 3-3, 7*9; distance 2"-$. Binary; period 
500 years. 

Variables. Chi: magnitude 4 to 14; period 409 days. A good 
comparison star when Chi is near maximum is its companion 
Eta (4-03). 

W: magnitude 5*0 to 7-0; irregular. An M-type variable. It 
lies close to Rho (4 -2). 

X: magnitude 6-o to 7*0; period 16-4 days. A Cepheid, 
lying close to Lambda (4-5). 

The famous variables U, R and SS Cygni are described in 
Appendix XXVIII. 

XebuU and Clusters. There are many nebular objects in 
Cygnus. One of the most striking is M.39, near Rho, a good 
open cluster and a fine sight in a small telescope. 



vulpecula is a small constellation near Cygnus. It contains 
no star brighter than magnitude 4^. The most interesting 
object is M.27, the Dumb-bell Nebula, a planetary; it is dim, 
but is well worth looking at, even though a telescope of some 
size is needed to show it properly. It lies not far from Gamma 
Sagitte. Vulpecula, the Fox, was once known as Vulpecula 
et Anser, the Fox and Goose; but nowadays the goose seems to 
have been discarded — possibly the fox has eaten it ! 

delphinus. A beautifully compact little group, very easy to 
recognize. The brightest star is Beta (3*7}. The most interesting 
object is the double star Gamma; magnitudes 4-5, 5-5; distance 
10* -5; P.A. 270 . The primary is yellow, the companion green. 
The variables U and EU arc described on page 325. 

SAonTA. Another compact group; the brightest stars are 
Gamma (37) and Delta (3-8). It lies between Ahair and Beta 

EQiruLEUs. The chief star of this little constellation is Alpha 
(4*1). Delta is an excessively close double, and a rapid binary. 

peoasus. Most of this constellation, including the Square, is 
shown on Map X. The chief star in the present map is 
Epsilon {2 -3) , which is suspected of variability. Close to it lies 
the bright globular cluster M.15, a fine sight in a moderate 

aquarius also lies mainly in Map X. On the present map are 
Beta (2*9), Alpha (3-0), and two nebulous objects; the fine 
globular M.2, which I find fully resolvable with my 12^-in. 
reflector and which lies between Beta Aquarii and Epsilon 
Pegasi, and the beautiful planetary H.IV.i, which lies in the 
same low-power field as the orange star Nu Aquarii (4*5). 
Aquarius is a Zodiacal constellation. 

aquila. The chief star, Altair, is of the 1st magnitude, and 
is easy to recognize because it has a brightish star to either side, 
Beta and Gamma. As well as Altair, the constellation includes 
Gamma (2-7), Zeta(3-o), Theta {3*1}, Delta and Lambda (3-4) 
and Beta (3-9). The fine below Altair, made up of Theta, Eta 
and Delta, is very easy to identify. 



Variables. Eta: magnitude 3*7 to 4-5, period 7-2 days. A 
typical Cepheid. 
R: magnitude 5-7 to 12; period 300 days. Spectrum M. 

serpens. This constellation is divided into parts, Cauda (the 
body) and Caput (the head), separated by Ophiuchus. Caput 
is shown in Map IX. The brightest star in Cauda is Eta (3-2) ; 
the most interesting object is the fine double Theta, magni- 
tudes 4-5 and 4-5, distance 22*, P.A, 103 . This is a splendid 
object, and is easy to recognize, as it lies in a rather isolated 
position not far from Delta Aquilae. 

scutum. Though containing no star brighter than the fourth 
magnitude, Scutum lies in a rich part of the Milky Way, and 
shows some fine fields. There are several clusters. One of these 
is the "Wild Duck", M.11, one of the most beautiful open 
clusters in the sky, and shaped like a fan; it lies near Lambda 
Aquilae. M.26, close to Delta Scuti (4-7) is another good open 
cluster. It is well worth while to sweep this whole region with 
a low power. R Scuti is an interesting variable (page 326). 

Sagittarius. This is a large and bright constellation, but is 
always very low in England, and cannot be seen to advantage ; 
part of it never rises at all. The chief stars are Epsilon (1 -8), 
Sigma (2-1), Zeta (2-6), Delta (27), Lambda (2-8), Pi (2-9), 
Gamma (30), Eta (3-2) and Tau (3-3). Deneb, Altair and 
Sagittarius lie almost in a straight fine, with Altair in the 
middle; this is probably the easiest way to find Sagittarius. It 
can be quite conspicuous on summer evenings. Adjoining 
Sagittarius, but too far south to be seen in England, is the 
tittle constellation corona australis (the Southern Crown). 

Clusters and Nebula. M.17; the Omega or Horseshoe Nebula, 
near Gamma Scuti ; a fine object in a moderate telescope. 

M.8; the Lagoon Nebula, an easy object near Mu Sagittarii. 

M.22; a bright globular between Sigma and Mu, not far 
from Lambda. 

capricornus. Like Sagittarius, Capricornus is in the Zodiac, 
It is rather a barren group ; the chief stars are Delta and Beta 
(each 2-9). 

Double Stars. Alpha: magnitudes 37, 43; distance 376*. 
This is a naked-eye double, and is easy to find, as the line of 

t 289 




DO, • T 

Deneb " . C r I*** 19*+) 


y!e LYRA 


g^tDELPHlNUS ' P ^ 

fc Altair — "■""""* •» 




12 * 

h is «\ \ 





stars made up of Gamma Aquite, Altair and Beta Aquihc 
points to it. The fainter component is again double; 3-7, 
11; distance 7*; P.A. 158 , and the smaller component of this 
pair is again double, though a very difficult object. 

Beta j a very wide double. Magnitudes 31, 6; distance 205*, 
P.A. 290 . The fainter component is again double; distance 
1 '-3, P.A, 103 °, but the companion is rather faint (io-6) 
and is thus rather difficult in small apertures. 

hercules. A small part of Hercules appears in Map VIII, 
but most of the constellation lies in Map IX. The site of the 
1934 nova, DQ. Herculis, is marked. This is now a difficult 
object, and has been found to be a spectroscopic binary. It is 
described in the text. 


These are mainly summer groups, though the northernmost 
parts of Hercules and Bootes are circumpolar in England, 
Rough times of rising and setting for Antares, in Scorpio, are as 
follows : 

January 1st Rises 5 a.m., highest in daylight, sets in daylight. 
April 1 st Rises 1 1 p.m., highest 3 a.m., sets in daylight. 
July 1 st Rises in daylight, highest in daylight, sets 1 a.m. 

October 1st Rises in daylight, highest in daylight, sets in 

Arctums in Bootes is easily recognized, and is shown on Key 
Map I. Corona is also most conspicuous, and can hardly be 
mistaken. The other groups are less easy to identify, as they are 
of large area but contain few bright stars. Scorpio is of course 
an exception, but the most brilliant part of the constellation is 
always very low in England. 

bootes. The chief star is Arcturus; others are Epsilon 
(2-4), Eta (2-7), Gamma (3*0) and Delta and Beta (3*5). 
Arcturus is of type K, and is distinctly orange, 

Double Stars. Epsilon: magnitudes 2-5, 5*3; distance 3*, 
P.A. 340°. The primary is yellowish, the companion bluish. 



Zcta: magnitudes 4-6, 47; distance about 1 '-3, P.A. 135°, 
This is close and rather difficult. Binary, period 1 23 years. 

Xi: magnitudes 4-8, 6-9; distance 7**0, P.A. 344 . Binary, 
period 152 years, 

Delta: magnitudes 3-5, 78; distance 105*, P.A. 080 . A very 
easy object in a small telescope. 

Variables, W and R, which lie close to Epsilon. R varies from 
magnitude 6 to 13 in 225 days; W from 5-2 to 6, irregular. 

corona borealis. This beautiful htde constellation can 
hardly be mistaken, and it really does look rather like a 
"crown". The chief stars are Alpha (2-2) and Beta (3-7}. 
Despite its small size, Corona is rich in interesting objects. 

Double Stars. Eta: magnitudes 5-7, 5*9; distance 1", P.A. 
varies rather quickly, as the star is a binary with a period of 42 
years. It is rather close, and is thus not an easy object. 

Zeta: magnitudes 4-0, 4-9; distance 6 s -3, P.A. 303 °. A fine 

Variables. T: the peculiar nova-like variable. Usually it 
fluctuates between magnitudes 9 and 10, but it rose to 2 in 1866 
and to 3 in 1946. It is well worth watching, as a fresh outburst 
may occur at any moment* 

R : magnitude 5 -6 to 1 4. The well-known irregular variable, 
described in the text. 

S; magnitude 6 to 12, period 361 days. Spectrum M. 

Hercules. A very large but rather barren constellation. It 
occupies the area between Vega and Corona Borealis. The 
chief stars are Beta and Zeta (2*8), Alpha (variable), Pi and 
Delta (3-1), Mu (3-4) and Eta (3-5). 

Double Stars. Zeta: magnitudes 3-1, 5-6; distance about 1 *. 
P.A. alters fairly quickly, as the star is a binary with a period of 
34 years. 

Delta: magnitudes 3-2, 7-5; distance n % P.A. 208 . 

Alpha: magnitudes 3 (variable), 54; distance 4" -6, P.A. 
no". The brighter star is an Ms-type giant, reddish; the com- 
panion green. 

Variables. Alpha. One of the Betelgeux-type irregulars. It 
fluctuates between magnitudes 3 and 3^, and over about twenty 
years I have found no semblance of a period. The best com- 


star map IX 

parison stars for it are Kappa Ophiuehi (3 -42), Gamma 
Herculis (3-79) and Delta Herculis (3*14). 
g: magnitude 4*6 to 6-o. An M-type irregular, near Sigma 


S: magnitude 6 to 12-5, period 300 days. Spectrum M. It 
lies between Alpha Herculis and Beta Serpentis. 

Clusters. M.13. The famous globular; it lies between Zeta 
and Eta, and can just be seen with the naked eye under good 
conditions. It is very easy to find with a telescope, and in a 
moderate aperture is a glorious sight. 

M.92: another globular, between Iota and Eta. It is not 
unlike M.I3, but is far less prominent. 

Z5 : a small bright planetary nebula, in the triangle formed 
by Beta, Delta and Epsilon Herculis. It is said to have a bluish 
hue, though to me it always looks white, 

ophiuchus. This constellation lies between Vega and Antares. 
It contains some fairly bright stars: Alpha (2*1), Eta (2-5), 
Zeta (2-6), Delta (2-7), Beta (2-8), Kappa and Epsilon (3-2), 
and Mu and Nu (3-3), but it is not easy to identify at first 
sight, and it is relatively barren of interesting objects. There 
is a bright globular cluster, M.t9, near Theta, and roughly 
between Theta and Antares; but it is always very low in 
England. Ophiuchus is not classed as a Zodiacal constellation, 
but it does enter the Zodiac in the region between Scorpio and 

libra. Zodiacal, but a very dull constellation. The chief 
stars are Beta (2-6), Alpha (2-8) and Sigma (3-3) ; Sigma is also 
included in Scorpio, as Gamma Scorpionis. There are few 
interesting objects apart from the Algol-type eclipsing binary 
Delta Libree, which has a magnitude range of 4*8 to 6-2 and a 
period of 2*3 days. Beta Libne is a B8-type star, and is said to be 
the nearest approach to a normal "green" star. It certainly 
may have a slightly greenish tinge, though the colour is so 
elusive that many people will fail to detect it. Of course, some 
double stars have green components, and Nova DQ, Herculis 
was also green at one stage in its career. 

Scorpio. A splendid Zodiacal group, but never well seen in 
England; it is always low down, and its "sting" never rises at all. 



The chief stars, apart from Antares, are Lambda (i-6), Theta 
(1-9), Epsilon and Delta (2-3), Kappa (2-4), Beta (2-6), 
Upsilon (2-7), Sigma and Tau (2-8), Pi (2-9), Iota 1 and Mu 
(3-0), G (3-2) and Eta (3-3), but Lambda, Upsilon, Kappa, 
Iota, Theta and Eta are invisible in England. Regulus and 
Antares are on roughly opposite sides of Arcturus, with Arcturus 
in the middle, which is of help in identifying Scorpio ; Antares 
is also distinguished by its ruddiness, and by the fact that, like 
Altair, it has a fairly bright star to either side of it — in this case 
Tau and Sigma Scorpionis. 

Doable Stars. Antares has a companion of magnitude 5*1 ; 
distance 3*, P.A. 275 , The primary is of course red; the 
companion is green. It is a fine object. 

Nu: magnitude 43, 6-5; distance 41*; P.A. 335°, A wide, 
easy double. Each component is again double, but very close 
and difficult. 

Beta: magnitudes 2-8, 5-0; distance 1 *. There is a third star, 
magnitude 4-9, at 14*. 

Clusters. M.80. A splendid globular, lying roughly between 
Antares and Beta. 

M.4. An open cluster. The stars in it are not brilliant, but the 
object is not hard to find, as it lies close to Antares. 

serpens. The chief star in Caput is Alpha (2-6), R is an 
M-type variable; 5*7-14-4, 357 days. M.5, a bright globular, 
lies near Alpha. 







The chief group in this map is the Square of Pegasus, which 
in my view is much more difficult to identify than might be 
supposed, since most people expect it to be smaller and brighter 
than it really is. The best way to find it is by means of Cassio- 
peia, since Gamma and Alpha Cassiopeia point directly to it. 
The line from Merak and Dubhe through Polaris will also 
reach the Square if prolonged far enough across the sky. Very 
rough risings and settings are as follows: 

January ist Rises in daylight, highest in daylight, sets at 

April ist Rises 2 a.m., highest in daylight, sets in daylight. 
July ist Rises in daylight, highest 5 a.m., sets in daylight. 

October ist Rises in daylight, highest 11 p.m., sets 7.a.m, 

It is therefore at its best during the autumn. As is shown 
on Map VII, one of the stars of the Square is generally in- 
cluded in the neighbouring constellation of Andromeda (Alpha 
Andromedae= Delta Pegasi). Andromeda and Triangulum are 
described with Map VII. 

pegasus. An important constellation, but not so conspicuous 
as is generally supposed. Alpha Andromeda (2-1) is in the 
Square. The other chief stars of Pegasus are Epsilon (2-3), 
which is shown on Map VIII, Alpha (2-5), Beta (variable), 
Gamma (2-8), Eta (2-9) and Zeta (3-4). It is rather instructive 
to count the number of stars inside the Square visible with the 
naked eye; there are not very many of them. 

Double Star. Xi: magnitude 4-0, 12; distance 12*, P. A. 108 , 
A difficult double, owing to the faintness of the companion. It 
is a binary, with a period of about a century and a half. 

Variable. Beta: magnitude 2-3 to 2-8. An M-type irregular. 
Suitable comparison stars are Alpha (2-50) and Gamma 
(2 -84) . There is a very rough period of about 35 days. 

awes. Celebrated as being the First Constellation of the 
Zodiac. It is not, however, very conspicuous. It lies between 



Aldebaran and the Square of Pegasus, and has two fairly 
bright stars, Alpha (a-o) and Beta (3-7). 

Double Star. Gamma: magnitudes 4-7, 4-8; distance 8* -2, 
P. A. ooo c . A fine, easy double, very well seen with a small 
telescope. Rather unexpectedly, this is an optical double. 

pisces. The last constellation of the Zodiac, though owing to 
the precession of the equinoxes it now contains the First Point 
of Aries. It is large but faint, the brightest star being Eta (3*7). 
Pisces can be identified by the long line of rather faint stars 
running below the Square of Pegasus. 

Double Stars. Alpha: magnitudes 4-3, 5-3; distance i*"9, 
P.A. aga°. 

Zeta : magnitudes 4-2, 5-3 ; distance 24*, P.A. 060 °. 

CETUS. Part of this large constellation is shown in Map IV, 
and the chief star (Beta) in the key map. Beta can be found by 
means of the Square of Pegasus, since Alpha Andromeda and 
Gamma Pegasi point towards it. Its proper name, Diphda, is 
often used, and it is an orange star suspected of variability. 
Not far from it is the M-type semi-regular variable T, which is 
reddish, and has a magnitude range of from 5 to 7. Mira 
(Omicron), shown here, is described with Map IV. 

sculptor (a merciful abbreviation of the old name "Appa- 
ratus Sculptoris"). A very obscure constellation near Diphda. 
It contains no star as bright as the fourth magnitude, and no 
objects of interest to the amateur. 

Aquarius. Part of this Zodiacal constellation is shown in 
Map VIII, but most of it lies in the present map. The chief 
stars are Beta (2*9) and Alpha (3-0); (Map VIII); Delta (3-3) 
and Zeta (37). There is a striking group of orange stars 
centred round Chi (5-1); these are easy to identify, and make 
pleasing telescopic objects under a low power. 

Double Star. Zeta.: magnitudes 4-4, 4-6; distance t'-g, P.A. 
256 . A fine binary, with a period of 360 years. 

Variable: R, magnitude 6 to 11, period 387 days. An M-type 
long-period variable, not far from the star Omega* (4-6). 

piscis austrinus. This small group is also termed Piscis 
Australis. It contains Fomalhaut, of the ist magnitude, but no 



' \ TRIAr. 










other star as bright as magnitude 4. Fomalhaut can be found 
by a line drawn from Beta through Alpha Pegasi, in the Square, 
and continued towards the horizon. From England, Fomalhaut 
is quite conspicuous near midnight in the autumn months. 
European observers, however, never see it to advantage. From 
southern countries it is very prominent, and acte as a "guide" to 
the rather confused area of the Southern Birds shown in the 
map on page 319. 

Double Stars. Beta: magnitudes 4-4, 7-8; distance 30*, P. A. 
172 . 

Gamma: magnitudes 4*5, 85; distance 4*"3, P.A. 262 . 

Delta: magnitudes 4-3, io-6; distance 5", P.A. 240 . Rather 
difficult, owing to the faintness of the companion. 




Maps I to X have been drawn for observers who live in the 
northern hemisphere. In fact the maps are valid for latitudes 
well south of Europe, with certain modifications; but they do 
not, of course, apply to countries such as South Africa, Aus- 
tralia or New Zealand, In the southern hemisphere everything is 
"upside down", and it takes the northern visitor some time to 
become used to the change. For instance, Leo and Virgo appear 
inverted, so that the aspect is as shown in the diagram. 


For this book I have not thought it necessary to re-draw all 
the maps, because it is easy to re-orientate them. However, we 
have not yet dealt with the stars which are too close to the south 
pole to be seen from Australia. Moreover, we cannot use the Great 
Bear as a pointer, because it is to all intents and purposes out of 
view. Instead we have the Southern Cross, which is truly magnif- 
icent. We also have Orion, which is cut by the celestial equator 
and is thus to be seen from all populated parts of the world. 

The Southern Cross is the smallest constellation in the whole 
sky, but it is also one of the most striking. Let us admit that it is 
not in the least like a cross; it looks rather the shape of a kite. Of 
its four chief stars, three are brilliant; the fourth, Delta, is con- 
siderably fainter, and makes the pattern seem unsymmetrical. 

There should be no difficulty in identifying Crux, particularly 
as the brilliant pair of stars made up of Alpha and Beta Centauri 
is an ideal guide to it. Alpha Crucis (Acrux) is of the first mag- 



nitude; Beta and Gamma are between 1 and 1 \. Note, in passing, 
that Gamma is decidely red, whereas its neighbours are white. 

From South Africa, Crux can drop very low in the sky, as on 
spring evenings (that is to say, around November; remember 
that in the southern hemisphere summer occurs around 
Christmas-time, and midwinter in June) , From Johannesburg 
part of it actually sets briefly, though from places further south, 
such as Cape Town, it scrapes the horizon, and from much of 
New Zealand it is always to be seen. The maps given in the rest 
of this section may be regarded as valid for the whole of South 
Africa, Australia and New Zealand; the relatively slight 
latitude variations make no important difference. 

The first thing to learn from Crux is the position of the south 
celestial pole, which lies in a rather blank area. Simply follow 
the "longer axis" of the Cross, from the red giant Gamma 
through Acrux. After passing through the polar region, the 
line will arrive at Achernar, the brilliant leader of Eridanus. 
Clearly, Achernar and Crux are on opposite sides of the pole, 
and about the same distance from it — so that when Achernar 
is high up, Crux will be low down, and vice versa. 

Next, follow the "sweep" shown in Map XI. Beta Carinze in 
the now-dismembered Argo Navis is of magnitude 1 -8, and so 
is bright enough to be conspicuous; beyond it we come to 
Canopus, which is surpassed only by Sirius. Sirius itself lies well 
beyond Canopus, too far to be conveniently shown in this key 
map. Beware of the False Cross, which lies in Argo — partly in 
Carina and partly in Vela. In shape it is similar to Crux, but it 
is much larger, and its stars are not so bright. 

Close to Alpha Centauri is Triangulum Australe, the South- 
ern Triangle — one of the few groups to have been given an 
appropriate name. Alpha, the brightest of the trio, is of above 
the second magnitude, and is distinctly reddish. Follow a fine 
from Alpha Centauri through Alpha Trianguli Australe, and 
you will eventually come to the second-magnitude star Alpha 
Pavonis. Beyond lies Grus, the Crane, with its leader Alnair. I 
have given these stars in the key map because they are the most 
easily identified objects in an area which is rather confused and 
undistinctive apart from Grus itself. Alpha Pavonis is circum- 
polar from Australia, but Grus is not. During winter evenings 
{southern winter !} it is below the horizon. 



Various other groups can be found from Crux. For instance, a 
line from Acrux through Gamma will show the way to Corvus, 
so that to all intents and purposes Achernar, the south pole, 
Crux and Corvus are lined up. Acrux and Alpha Centauri act 
as approximate guides to Antares. And a line from Acrux 
passed midway between Beta and Gamma Crucis will end up 
somewhere near Spica in Virgo. Remember that the Y of Virgo 
is now upside-down by northern reckoning, and the Sickle of 
Leo curves "down" instead of "up". As soon as Spica and Leo 
have been found, the other well-known features such as Arcturus 
and Corona can be located by re-orientating the maps given 
earlier in this section. 

^.Scorpio 1 

Centjuriit »^£T .« 
y* *r ACRUX 

a^F Trtingulum ^ 
/ Auitnle 1 ^ 

f p CARINit^ 

fc Vclorum 


r i 

1 l p "ppi» 

/ J 

/ 1 

' SOUTH + 
' POLE 1 

4 i 















+. + 

Can is Major 


1 + 4 





• • 




• \ 






Orion is on view for a large part of the year — all through the 
hot season — and is out of view only during the winter. Now, of 
course, Eigel is at the "top" and Betelgeux at the "bottom"; 
the Belt stars point downward to Aldebaran and upward to 
Sinus. Ganopus can be located by using Zeta and Kappa 
Ononis, and Ganopus and Sirius point to the Twins, Castor 
and Pollux. Regulus and the Sickle can be found by taking a 
"sweep" from the lower part of Orion through Procyon, as 
shown in the key map. Canopus is not circumpolar from South 
Africa or most of Australia, but it spends litde time below the 






This map covers a brilliant region of the sky, crossed by the 
Milky Way. In addition to the Crux-Centaurus area it includes 
the whole of Sagittarius and most of Scorpio. Both these groups 
are much more splendid than European dwellers appreciate; 
when Scorpio is almost overhead it is a magnificent sight. 

crux is pre-eminent. Its chief stars are Alpha or Acrux (com- 
bined magnitude 0-9), Beta (1-3), Gamma (i-6) and Delta 
(3-1); there is also Epsilon (3-6) which tends to upset the 
pattern. Though there is so little difference between Beta and 
Gamma, Beta is unofficially ranked as of the "first magnitude", 
while Gamma is not. Binoculars will show a striking difference 
between Gamma, a Red Giant of spectral type M, and the 
remaining members of the Gross, all of which are hot and white. 

Double Stars. Alpha (Acrux) ; magnitudes 1 -6, 2 • 1 ; distance 
4*7; P.A. 1 1 4 . This is a splendid double, separable with a 
small telescope (it is very easy in a 2-inch) ; there is also a third 
star in the field. 

Gamma: 1 -6, 6-7; distance 1 io"-6; P.A. 03 1°. A wide optical 

Iota: magnitudes 47, 7-8; distance 26* -4; P. A 02 7 . Very 

Mu: magnitudes 4*3, 5-5; distance 34'-g; P.A, 01 7 , Also 
very easy. 

Variables. R: magnitude 6 to 8; period 5-8 days; a Cepheid. 

S: 6-6 to 77; period 47 days; also a Cepheid. 

T: 6-9 to 77; period 67 days; yet another Cepheid. All 
these three Cepheids may be foUowed with binoculars. 

Clusters and Nebula. Kappa Crucis, the so-called Jewel Box, is 
a superb loose cluster in which there are stars of different 
colours. It is easily identifiable in binoculars, and I have no 
hesitation in calling it the most glorious cluster in the whole sky. 
Close to it is the celebrated dark nebula called the Coal Sack, 
again visible in binoculars. There are a few foreground stars, 
but the dark mass is really striking. Crux may be the smallest of 
all the constellations, but it is amazingly rich in interestingobj ects. 

o 305 


centaurus. This is another really splendid constellation. Its 
leading stars are Alpha (combined magnitude -0*3), Beta 
(Agena) (0-7), Theta (s*a), Gamma (2-3), Eta (2-6), Epsilon 
(2-6), Iota (2-9), Delta (2-9), Zeta (3-0), Kappa (3-3), Mu 
(3-3) and Lambda (3'3). Alpha Centauri is striking; it is 
surprising that it has no old-established official name. It makes 
up a magnificent pair with Beta or Agena. Centaurus has a 
distinctive shape, and more or less surrounds Crux, 

Double Stars. Alpha; magnitudes 0-3, 1-7. This is a superb 
binary with a period of 80 years. Both position angle and dis- 
tance alter fairly rapidly, but the average separation is about 
4*, so that the pair is easily split in a small telescope. Beta has a 
qth-magnitude companion at PA. 255°, but the distance is only 
1 "-4. Gamma is a close binary; the components are almost 
equal (magnitudes 3-1, 3-2) and the period is 84! years. 

Variables. R: magnitude 5-4 to 11 -8; period 547 days. A 
typical long-period variable of the Mira type. 

T: magnitude 5-5 to 9-0; period 91 days. This is classed as a 
semi-regular variable. 

Clusters and Nebulm. Omega Centauri is much the finest 
globular cluster in the sky. To the naked eye it appears as a 
hazy star of the 4th magnitude; binoculars show it well, and a 
fairly small telescope will resolve it. 

NGG 3766. A fine open cluster near Lambda, visible with 

circinus. A small constellation between Alpha Centauri and 
Triangulum Australe. Its leading stars are Alpha (3-4) and 
Beta (4-2). Alpha is a double; magnitudes 3-4, 8-8; distance 
1 5* -8, P. A. 235 . The primary is of spectral type F, and is 
distinctly yellowish. 

norma. A very obscure constellation; the brightest star, 
Gamma 2 , is only of magnitude 4-1. The only object of note is 
the open cluster NGG 6067, which is 20' in diameter, but is not 
particularly conspicuous. 

Triangulum australe. A prominent triangle, made up of 
Alpha (1-9) and Beta and Gamma (each 3-1), Alpha is 
obviously reddish. 

Variable. S : magnitude 6-4 to 7 -6; period 6-3 days. A Gepheid. 

Cluster. NGC 6025. A bright open cluster, visible in bino- 





Ara. A fairly prominent constellation; the leading stars are 
Beta (a-8), Alpha (3-0), Zeta (3-1), Eta (3-7), Delta (3-8) and 
Theta (3 -9) . There are no notable objects except for two Algol 
variables; R (6*o to 6*9, 4-4 days) and RW (8-7 to 12, also 
4-4 days). 

lupus. This is a decidedly "shapeless" constellation, adjoin- 
ing Gentaurus. It contains some moderately bright stars, of 
which the chief are Beta (2-8), Alpha (2-9), Gamma (2-9), 
Delta (3-4), Zeta (3-5) and Phi 1 (3-6). 

Double Stars. Kappa: magnitudes 4*1, 6*0; distance 27*; 
P,A. 1 44 . Very wide and easy. 

Eta: magnitudes 3-6, 7-7; distance i5**2; P.A. 02 i°. Also 

Pi: magnitudes 4-7, 4-8; distance 1*7; P.A, 076 . 

Mu: magnitudes 5-0, 5-2; distance i*^: P.A. 146 . 

telescopium, A small constellation adjoining Ara, The lead- 
ing stars are Alpha (3-8) and Zeta (4-1). It contains nothing of 

corona australis. A small semicircle of stars, of which the 
brightest are Alpha (4-1) and Beta (4-2). Gamma is double; 
magnitudes 5-0, 5-1; distance 2*7; P.A. 054 , Though its stars 
are faint, Corona Australis is easy to recognize, and is worthy of 
separate identity instead of being included in Sagittarius. 

Also on this map are parts of scorpio and ophiuchus, and all 
of Sagittarius. The southernmost parts of Scorpio and Sagit- 
tarius are not easily visible from Europe — which is a pity, 
because Scorpio at least is a splendid constellation. The "sting", 
made up of Lambda (1-7), Kappa (2*5), Upsilon (2-7), Iota 1 
(3*1) and G (3-2) is very distinctive, and close by lies Theta 
(2*0), The two open clusters M6 and M7 are worth studying. 
The brightest star in Sagittarius, Epsilon (1 -8), lies not far from 
the Scorpion's sting. Observers who live in Europe or North 
America cannot be expected to appreciate how brilliant and 
distinctive Scorpio and Sagittarius really are. 






This map is occupied by Argo Navis, which has now been 
divided up into smaller constellations. Crux, Beta Carina:, 
Canopus and Sirius form a magnificent curved line which 
cannot be mis-identified. The False Cross is made up of Epsilon 
and Iota Carinas, and Kappa and Delta Velorum. The whole 
region is exceptionally rich, and is crossed by the Milky 

carina. This is the most brilliant part of Argo, and contains 
Canopus, which is inferior only to Sirius. Canopus has an F- 
type spectrum, and is usually described as yellow, though I 
admit that to me it always looks colourless. Its magnitude is 
- 07. The other leading stars of Carina are Epsilon (1 7), Beta 
(i-8), Iota (2-2), Theta (3-0), Upsilon (3-1), Omega (3-6), Chi 
(3*6), and p (3*6). Most of them are hot and white, but Epsilon 
is a beautiful orange star of type K. The small constellation 
of Volans intrudes into Carina. 

Double Star. Upsilon: magnitudes 3-1, 6-o; distance 4* -6; 
P.A. 126 . 

Variables. Eta: the most erratic of all variables, once the rival 
of Canopus and now below magnitude 7. It lies in a particularly 
rich area, and may at any time regain prominence. 

R: magnitude 3*9 to io-o; period 308-6 days. A Mira-type 

S: magnitude 4-5 to 9-9; period 149*5 days. Also of the Mira 

1: magnitude 3-6 to 5-0; period 35-5 days. A Cepheid, Its 
long period (by Cepheid standards) indicates very high 

U : magnitude 6-4 to 8-4 ; period 38 -8 days. Another Cepheid, 
also with a period of unusual length for a star of its type. 

Clusters and Nebula. Carina is well supplied with rich fields, 
and the nebulosity associated with Eta is worthy of special note. 
NGC 25 1 6, near Epsilon, is a rich open cluster visible with the 
naked eye; NGC 2808 is a good example of a globular. 

vela. Principal stars: Gamma (1-9), Delta (2-0), Lambda 
(2-2), Kappa (2-6), Psi (3*6), and c, Phi and Omicron (each 
37). Gamma is the brightest of all the Wolf-Rayet stars. Kappa 



and Delta make up part of the False Cross, together with 
Epsilon and Iota Carina:. 

Double stars. Gamma: magnitudes 2-2, 4-8; distance 41*; 
P,A. 220°. Very wide and easy. Each component is itself a 
spectroscopic binary. 

Delta: magnitudes 2-0, 6-5; distance 2* -9; P,A. 164 . Easy. 

Mu: magnitudes 2-8, 7*0; distance i*-o; P.A. 079 . 

Psi: magnitudes 4-2, 47. P.A. and distance alter quickly, as 
this is a binary with the relatively short period of 34*1 years. 
The mean separation is about o**4, so that this is too close a 
pair to be easy. 

Variables. There are two short-period variables within bino- 
cular range. AH is a Cepheid (magnitude 5*8 to 6*4; 4*2 days), 
while AI is an RR Lyra; type star with a range of 6 -4 to 7 ■ 1 and 
a period of only 0-1 1 days. In addition, N Velorum, which is of 
type K5 and is distinctly reddish, is a suspected variable well 
worth watching; it lies close to the False Cross. Its official 
magnitude is rather above 5. 

Clusters. There are several open clusters in Vela, though none 
is of special note. The whole area is extremely rich, and is well 
worth sweeping with binoculars. 

pupfis. This is the northernmost part of Argo, and part of it is 
visible from European latitudes. The principal stars are Zeta 
(2-3), Pi (27), Rho (2-9), Sigma (3-2), Nu (3-2) and Xi (3-5). 
Zeta is another very hot star of spectral type O. 

Double Stars. Sigma: magnitudes 3*2, 8 -5; distance 22 '-4; 
P.A. 074°. 

Xi: magnitudes 3-5, 13-5; distance 4**3; P.A. 189 . 1 include 
this as an example of a really difficult object, in view of the 
faintness of the companion. 

Variables. L a . This is an ideal binocular object. The range is 
from 2-6 to 6-0, but it is a semi- regular variable (period 141 
days) and the light-curve never repeats itself exactly. It is a red 
giant of type M. Suitable comparison stars are L 1 (magnitude 
5"0)» C (5*3), I (4*5) and Sigma (3-2). 

V: magnitude 4-5 to 5-1; period 1*45 days. An eclipsing 
binary of the Beta Lyrae type, near Gamma Velorum. 

Z: magnitude 7-2 to 14*6; period 510 days; Mira type. 

Cluster. M. 46; in the northern part of Argo, and described on 
page 277. 





pyxis. A small group, with only Alpha (37) above the fourth 
magnitude. The only object of interest is T, a recurrent nova 
which is usually of about the 14th magnitude, but which 
increased to 7-0 in 1920 and again in 1944. 

antlia. An even less remarkable constellation. The brightest 
star is Alpha {magnitude 4*4), and there are no noteworthy 

volans. A constellation which intrudes into Carina, near 
Beta. The chief stars are Beta (37), Zeta (3*9), Gamma 3 (3-9), 
Delta (4-0) and Alpha (4-2). 

Double Stars. Gamma: magnitudes 3-9, 5-8; distance 13* -8; 
P.A. 299 . Very wide and easy. 

Epsilon: magnitudes 4*5, 8-o; distance 6*-i ; P.A. 02 2°. 





This is the south polar area. It is divided up into a number of 
relatively dim constellations. Broadly speaking, the region is 
enclosed by imaginary lines connecting Canopus, Achernar, 
Alpha Pavonis and Alpha Trianguli Australe. As has been 
shown on the key map, the pole may be located by using the 
longer axis of Crux as a guide. 

OCTANS. A remarkably barren constellation. The brightest 
star is Nu (magnitude 37} ; Sigma, which lies close to the pole, 
is only of magnitude 5-5. The only object worthy of mention 
is the long-period variable R (6-4 to 13-2; 405 days, Mira 

apus. Fairly compact; the leading stars are Alpha (3-8) and 
Gamma (3-9). 

Variable. Theta; magnitude 5-1 to 6-6. The spectrum is of 
type M, so that the star is red. It seems to be genuinely irregular 
in behaviour. 

MUSCA. This is a conspicuous litde constellation adjoining 
Crux. It contains some fairly bright stars, closely grouped. The 
leaders are Alpha (2-9), Beta (3-2), Delta (3-6), Lambda (3-8) 
and Gamma (4'0). 

Double Stars. Beta; magnitudes 3-9, 4-2; distance T-6; P.A. 
007 . A good example of a pair with almost equal components. 
Theta: magnitudes 5-6, 7-2; distance 5 '7; PA. 186 . 
Variables. R: magnitude 6-3 to 7-3; period 7-5 days. A 
S: magnitude 6-2 to 7*3; period 97 days. Another Cepheid. 
chameleon. Very obscure, with no stars brighter than Alpha 
and Gamma (magnitude 4*1). Delta is made up of a pair of 
stars, of magnitudes 4-6 and 5-5 respectively; the brighter is 
white, the fainter orange. However, the separation is too wide 
for classification as a double, and the two are not genuinely 
associated with each other. 

mensa. This would be one of the most unremarkable of all 
constellations but for the presence of the Large Cloud of Magel- 
lan. The brightest star in Mensa (Gamma) is only of magnitude 
5- 1, but the Cloud is superb; it has been described in the text. 



Binoculars show it excellently, but it is of course a prominent 
naked-eye feature. It extends from Mensa into Dorado. 

hydrus. Chief stars: Beta (2-9), Alpha (3-0) and Gamma 
(3-1). Alpha lies close to Achernar. Though it has three fairly 
bright stars, Hydrus is remarkably deficient in interesting 

reticulum. Another group which is compact enough to be 
easily identifiable; its leaders are Alpha (3-4) and Beta (3-8). 

Double Star. Theta: magnitudes 6-2, 8*3; distance 3* -9: P.A. 

Variable. R: magnitude 6-8 to 14*0; period 278 days. Mira 

dorado. A constellation notable chiefly for containing part of 
the Large Cloud of Magellan. Its brightest stars are Alpha (3-5) 
and Beta {a variable; at maximum, 3-8). 

Variable. Beta; magnitude 38 to 5-0; period 9-8 days; a 

Nebula. The Large Cloud has already been described, but 
mention should be made here of the Looped Nebula, 30 
Doradus, which is visible to the naked eye in the Cloud. With 
any optical aid it is a superb sight. 

piCTOR. A constellation between Dorado and Canopus; its 
leader is Alpha (3-3). 

Double Star. Iota: magnitudes 5-6, 6-4; distance 12*: P.A. 
058 . 

Variables. R: magnitude 6*7 to 10*0; period 171 days. Semi- 

RR. In 1925 the bright nova RR Pictoris flared up here. It 
became very prominent, but is now extremely faint, and there is 
no prospect of its undergoing a second outburst, 

eridanus. Part of Eridanus is shown in this map ; of course the 
most brilliant star, Achernar, is much too far south to be seen 
from Europe. Also in the southern part of the constellation is 
Theta, a splendid double; magnitudes 3-4, 4-4; distance 8*-5; 
P. A. 088 . To the naked eye Theta appears of magnitude 3*1, 
but the ancient observers ranked it as of the first magnitude, 
and it may have faded since then, though the evidence is very 
far from conclusive. Both components are of spectral type A2. 
horologium. A very obscure group adjoining Eridanus; its 
only moderately bright star is Alpha (3-8). In it is the long- 







period variable R, which varies between magnitudes 47 and 
14-3 in 402-7 days, and is of the Mira type. 

Also included in this map are Phoenix, Tucana and Pavo, but 
these are best described with Map XVI. Note that the Small 
Cloud of Magellan adjoins Hydrus and actually extends into it, 
though most of it lies in Tucana. 



This is the region of the "Southern Birds". I have found that 
the best means of identification is to locate Alpha Pavonis by 
using Alpha Ccntauri and Alpha Trianguli Australe, as shown 
in the key map. Of all the groups, only Grus is distinctive. 

pavo. The brightest star is Alpha (2-1); then follow Delta, 
Eta and Beta (each 3-6), and Kappa (4-0 at maximum). Alpha 
is rather isolated from the rest of the constellation. Delta is 19 
light-years away, and is very like the Sun in every respect; it is 
interesting to speculate as to whether it has a similar system of 
planets ! 

Double Star. Xi: magnitudes 4-3,8-6; distance 3 "-3 ; P.A. 151 . 

Variables. Kappa; magnitude 4-0 to 5-5; period 9*1 days. 

R. S, T. All these are of the Mira type. R: 7-5 to 13-8, 230 
days. S: 6-6 to 10-4, 387 days. T: 7-0 to 14-0, 244 days. 

indus. A group near Alpha Pavonis. Its leaders are Alpha 
(3-2) and Beta (37). The only object of note is the double star 
Theta; magnitudes 4-6, 7-0; distance 5 '-3; P. A. 276°. 

tucana. The Toucan is enriched by the presence of the Small 
Cloud of Magellan as well as the superb globular cluster 47 
Tucanae. Chief stars: Alpha (2-9), Beta (37), Gamma {4*1} and 
Zeta (4-3). Alpha Tucana:, Alpha Pavonis, and Alnair (Alpha 
Gruis) form a triangle. 

Double Stars. Beta: magnitudes 4-5 and 4-5, giving a combined 
naked-eye magnitude of 3-7; distance 27*- 1, P.A. 170 . A 
superb easy pair. Each component is again double, though in 
each case the separation is small. In the same field is yet another 
star, of magnitude 5, which is itself double. The group is very 
well worth careful study. 

Delta: magnitudes 4-8, 9-3; distance 6"-8; P.A. 283 . 

Kappa: magnitudes 5-1, 7-3; distance 5*7; P.A. 341 . 

Clusters and Nebula. The Small Cloud lies almost entirely in 
Tucana, and it too is a prominent naked-eye object, though 
moonlight will drown it. On its fringes are two splendid globu- 
lars. 47 Tucanee is surpassed only by Omega Centauri, since it is 
easy to see with the naked eye and is magnificent with any 
optical aid. Also close to the Cloud is NGC 362, which is just 



visible with the naked eye, and has a diameter of 10 minutes 
of arc. 

grus. A very prominent and distinctive constellation which 
really does give some impression of a flying crane ! Its chief 
stars are Alpha or Alnair (2-1), Beta (2-2), Gamma (3-1) and 
Epsiion (3-7), Alnair and Beta make a good contrast, since 
Alnair is white and Beta is orange-red. In the line of stars 
extending from Beta to Gamma are two pairs, Delta 1 and Delta 2 , 
and Mu 1 and Mu a . Both are easy to separate with the naked 
eye, and are too wide to be classed as bona-fide doubles. 

Double Star. Theta; magnitudes 4-5, 7-0; distance i"-5; P.A. 
052 . 

Variables. R: magnitude 7-4 to 14-9; period 332-5 days; Mira 

S: magnitude 6-o to 15; period 401 days; also Mira type. 

phcenk. A less obvious group, extending to the region bet- 
ween Grus and Achernar. It has one bright star, Alpha or 
Ankaa (2-4); then follow Beta (3-3), Gamma (3-4) and Delta 

Double Stars. Beta; magnitudes 4-1, 4-1; distance l # f| P.A. 

Zeta; magnitudes 4 (variable) and 7-2; distance o*-8; P.A. 

Eta; magnitudes 4-5, 11-4; distance 19' -8; P.A. 21 6°. Not 
easy, because of the faintness of the companion. 

Variables. Zeta; magnitude 3-6 to 4-1, period 1-67 days. An 
eclipsing binary. 

R: magnitude 7-5 to 14-4; period 268 days. Mira type, 

S: magnitude 7-4 to 8-2; period 141 days. Semi-regular. 

SX: magnitude 6-5 to 7-5 ; period 0-055 days. RR Lyrae type. 

microscopium. An entirely obscure constellation, adjoining 








■Gfc 7V 


jL/TRIAt 1 




' R 







Appendix XXVIII 


The observation of variable stars is becoming more and 
more popular among amateurs. Some notes on it have already 
been given (Chapter 15). To present a full account would 
need a complete book to itself, particularly as there are so many 
variables within range of a small telescope; clearly this is 
impossible here, but I can at least provide some "typical cases" 
to suit various types of equipment. I have done my best to give a 
general survey, though I admit to having confined myself in the 
main to stars which are on my own observational list. First, 
however, it may be as well to summarize the various classes : 

Eclipsing variables. These, as we have seen, are not true variables 
at all, but are binary systems. The main types are: 

1. Algol. One component much brighter than the other, pro- 
ducing one marked minimum and a second minimum which is 
too small to be noticeable. 

2. Beta Lyne. Components less unequal, and very close together; 
both minima noticeable. 

3. W Ursae Majoris. Close binaries; components often about 
equal to the Sun; short periods, often less than 12 hours. No 
bright examples. 

To study eclipsing binaries properly needs photoelectric 
equipment, which few amateurs will have. In fact, there are 
some stars in which visual work is useful ; but they are rare, and I 
have never tackled them myself, which is an extra reason for 
saying no more about them here. 

Pulsating Variables, (a) Short period 

1. RR Lyra 3 ; stars. Very regular; very short periods; common in 
globular clusters, though many of them (including RR Lyra; 
itself) are not cluster members. No bright examples. All RR 
Lyrae stars are of approximately the same luminosity, so that 
they act as distance-gauges, 



2. Cepheids, such as Delta Cephei, Eta Aquike and Beta 
Doradu s. Already described in the text. Some have a consider- 
able range in magnitude ; others change very little. For instance, 
Polaris is a Cepheid, but its range amounts to less than 0-2 
magnitude. The changes are very regular, and again photo- 
electric equipment is needed. Classical Cepheids belong to 
Population I. 

3. W Virginis stars. These are Population II Cepheids, with a 
rather different period- luminosity law. About 50 are known, 
but none is brilliant in our skies. Again, photoelectric equipment 
is needed. 

There are various other classes of regular short-period vari- 
ables, but I do not propose to discuss them here, because they 
are not suited to amateur observation. 

(b) Longer period 

1. Mira-type stars, such as Mira Ceti, R Cygni, Chi Cygni and 
U Orionis. Both period and range alter, and the light-curve is 
never repeated exactly from one cycle to the next. Most of them 
are Red Giants. Because they are unpredictable, they are ideal 
amateur objects; it is quite good enough to estimate their 
magnitudes down to o*i. 

2. Semi-regular stars, such as R Lyrae. Smaller ranges, and 
periods which are generally shorter; but the periods are very 
rough indeed, and are subject to interruption. Amateur observa- 
tion of them is very valuable. 

3. RV Tauri stars. Alternate deep and shallow minima, but the 
light-curves are never repeated exactly, and the behaviour is 
often quite irregular for a while. R Scuti is the brightest 

(c) Irregular 

This is a general term ; some stars which are classed as irregular 
may in fact be semi-regular, but insufficiently observed. A 
splendid example is Rho Cassiopeiae. Mu Cephei, Herschel's 
"Garnet Star", also seems to be quite irregular. 

Eruptive Variables 

1. SS Cygni or U Geminorum stars. Nova-like outbursts at 
mean intervals which range from 20 to 600 days, but which are 
never predictable. Ideal for amateur observation, but most of 
them are rather faint, and large apertures are needed. 

w 321 


2. R Coronae stars. These remain at or near maximum for most 
of the time, but exhibit sudden, unpredictable drops to mini- 
mum. They contain more than their fair share of carbon, but 
are deficient in hydrogen. Observation of them is very useful. 
Only R Coronae itself is ever visible with the naked eye; stars of 
this type are rare, and most of them are inconveniently faint. 

3. T Tauri stars. Rapid, irregular fluctuations. These seem to be 
very young stars, but most are faint; T. Tauri itself is the 
brightest of its class (mag. about 9) . 

4. Z Camelopardalis stars. Similar to SS Cygni stars except that 
at unpredictable intervals the fluctuations cease for a while, and 
there is a "standstill". Rare; large apertures needed. 

5. Flare stars, such as UV Ceti and AD Leonis. These show 
sudden rises amounting perhaps to several magnitudes; the 
outburst takes only a few minutes, and the subsequent fading 
may take hours. Again, most of them are faint, and the observa- 
tion technique is different from that used for other variables; 
the star is kept under constant observation for a set period. I 
have spent many tens of hours in observing them, but I have 
only seen one "perform". This was AD Leonis, which is easy to 
find because it lies in the field with Gamma Leonis. Its normal 
magnitude is 9-5, but it can flare up to above 9. UV Ceti, the 
prototype, is usually I2*g, but on one occasion was seen to 
increase to 5-9! All these stars are nearby red dwarfs. Observa- 
tion of them is fascinating, but is a matter for the real specialist 
with endless patience. 

6. P Cygni stars. Slow, erratic variations; may be related to 
novae. The only bright example is P Cygni itself, which is some- 
times classed as a nova (1600) but since about 1715 has 
remained of about the fifth magnitude. All are extremely hot, 
luminous and remote. 

7. Novae. Rapid rise, followed by a slower decline. The out- 
standing examples of recent years have been HR Delphini 
(1967), and Nova Cygni (1975). 

When estimating the magnitude of a variable, it is essential to 
use several comparison stars. Either the step-method or the 
fractional may be employed (see pages 1 85-6) . (I use the step, 
though many people tell me that the fractional is actually 
rather more accurate.) What usually happens, of course, is that 
a discrepancy is found. Suppose you estimate the variable as 



being 0-3 below comparison star A, and 05 above B; on looking 
up your charts you find that A is of magnitude 7-0, B is 7*6. 
From A, the variable would work out at 7-3; from B, 7-1. By 
using three or more comparison stars a good figure can usually 
be obtained, but odd things can happen sometimes; on more 
than one occasion a comparison star has been found to be itself 
variable, which leads to very peculiar results ! Unfortunately, it 
is not easy to compare a red star with a white one, and many 
long-period variables are red. U Cygni, which is intensely red, is 
notoriously difficult to estimate correctly, as I know to my cost. 

The following notes and charts are specimens only. Anyone 
who is interested can obtain others; if he belongs to the British 
Astronomical Association or the American Association of Vari- 
able Star Observers, there will be no difficulty in this respect. 
Binocular variables are dealt with on pages 324 to 327 and 
telescopic variables on pages 328 to 334. 




Many interesting variables are within the range of binoculars, 
and there are a few which can be estimated with the naked eye 
— though extinction must always be allowed for. Naked-eye 
variables are Betelgeux, Alpha and Gamma Cassiopeise, Alpha 
Hcrculis, Delta Cephei, Kappa Pavonis, Beta Doradus and 
various others; the comparison stars can be looked up from the 
maps and notes in the previous section. 

If only one pair of binoculars is available, a good pair may be 
7 x 50 (magnification 7; diameter of each O.G., 50 mm). With 
magnification of over 12 or so, it is a good idea to have a 
mounting, which can easily be made. For my 20 x 70 binoculars, 
I made a stand out of a plank and broomhandles, which is 
rudimentary, but which works well. 

R Lyra. Semi-regular. 4-0 to 5-0. Comparison stars, Eta and 
Theta (4-5) and 16 (5*1). The period is said to be about 46 days. 
An awkward star, because there are no suitable comparisons 
close to it; but it is very easy to find. Do not be surprised if 
your light-curve seems odd ! 







1 7=4'5 



(NaJud-eye mew) 



U and EU Delphini, U has a range of 5-6 to 7-5; irregular. EU 
ranges from 6*0 to 6-9; semi-regular, period around 60 days. 
Comparisons : A {5 *6, but inconveniently far away) ; B (6 -3) , D 
(6*3) ; H (6-8) ; and G (7-3). HR, the 1967 nova, is now too faint 
for binocular use. 


29 Vulpeculae 


• •< 

# ®HR 







A = 5-6 
B=6- 3 
D = 6- 3 
H = 6-8 
G = 7-3 







WCygni. A very interesting star. The range is 5*0 to 7 *6, and it is 
officially classed as semi-regular with a period of 130 days, 
though my own observations since 1968 certainly do not con- 
firm this. To locate it, find Rlio Cygni (map, page 290). The 
field will be instantly recognizable in binoculars. Comparisons : 
75 Cygni ( 5-0), D (5-4), A (6-i), B (67), K (6-8), L (7-5). 
Beware of the star marked X, which is itself variable by half a 
magnitude. (Note that the letters in these charts are those used 
by variable star observers, and are not "official"; for instance, 
X Cygni, near Lambda, is a Cepheid, and is not the same as the 
X on this chart.) Note 75 Cygni. I shall return to it later, as it is 
the guide to another famous variable, SS Cygni. 


A Aquilze 




c © R 
K * G -M 



{Naked-eye or 
binocular view) 

A=4"5 F«-6*i 
B-48 G = 6-8 
C = 5«o H = 7-i 
D=5-a K-77 




E = 5-6 



p Cygni 



{Naked-eye or 
binocular oiew) 

75 Cygni ==50 
D = 5'4 
A = 6-i 
Ki"6 - 8 

* 75 Cygni 

R ScutL The brightest of the RV Tauri stars. Range 5 to 7; 
rough period 144 days. It is easily found from Lambda Aquilse 
and the famous "Wild Duck" cluster M.n (page 290). Com- 
parisons: A (4-5), B (4-8), C (5-0), D (5-2), E (5-6), F (6-i), 
G (6-8), H (7-1), K (77). R makes a well-marked quadrilateral 
with F, G and H. 

Rko Cassiopebe. Close to Beta (page 284). An ideal binocular 
object. Its usual magnitude is about 5, but its official range is 
4*1 to 6*2; its drops to minimum are infrequent (I have never 
seen one yet), and nobody knows what sort of variable it is. It is 
a very remote super-giant. Comparisons : Theta (4-5 ; page 284) , 
Sigma (4-9), Tau (5-1), H (57), K (6-1). 

These are only half a dozen of the many variables which may 
be followed with binoculars. Also, some long-period variables, 
such as R Leonis, U Orionis and R Serpentls, are binocular 
objects when near maximum j and Mira Ceti, of course, is a 
naked-eye object when at its best. In 1969 it even approached 
the second magnitude. 







{Naked-eye or 
binocular view) 




= 5*7 
■ 6-i 








Again I give only a few specimen examples and charts. There 
are so many variables within range of even a 6-inch telescope 
that no single observer can hope to deal with them all, and one 
has to make out a personal list. My own (1970) includes 51 
stars, which is as many as I can manage ; others will certainly be 
able to do better. The following charts are inverted, for tele- 
scopic use. 

R Cygni. This is extremely easy to find, since it lies in the field 
with the 4th-magnitude star Theta Cygni— just off the map on 
page 290, but shown here. It has a range of from 6 "5 to 14-2, 
and a period of 426 days. At its brightest it is extremely easy, 
and is visible in binoculars; at minimum it needs a large 

Theta Cygni is easily found ; near it is the comparison star 2 
(6-6). Other comparison stars are 5 (9-0), 14 (9-9), 31 (n*o), 
36 (11-4), 43 (U'9), 59 (12-3) and x (12-8). This is not a full 
sequence, but it will be enough to show the way in which R 
Cygni behaves. It is of type S, and very red. Of course, it passes 
below the range of small telescopes when faint. 





•r) " -3^- Vega 

•9 8. & 



(guide star for 
R Cygni) 

{Naked-eye or 
binocular view) 



FIELD for 

{Telescopic view) 

2 = 6-6 36 ■=• 1 1 -4 

5=9-0 43 = 11 -9 

H=9"9 59 = i2-3 

I 30-10-5 x = ia-8 

31 -109 












SS Cygni. This is an excellent example of a fainter variable which 
is easy to find. Locate 75 Cygni, near Rho, as already described; 
it is identifiable because it is distinctly red. Then look for the 
triangle made up of C (8 -5), G (9 -6) and F (g -4} ; SSlies between 
C and G. Also to hand are A (8-o), N and 49 (each 1 1 -3), O 
(11 -8) and P (12-1). At its usual brightness SS is comparable 
with O ; at its best it can equal A. The average period between 
outbursts is 50 days, but this is only an average. Apparently all 
SS Cygni stars are spectroscopic binaries. 



A = 8-o 
C=8- 5 
F = 9 -4 
G = 9-6 

= n-8 

P = I2"I 



SS CYGNI (Telescopic view) 

R Leonis. Range 5-4 to 10*5; period 313 days; Mira type. It lies 
near Regulus, and makes up a trio with 18 Leonis (5-8) and 19 
(6 -4). Other comparison stars are 21 Leonis (6-6), M {7-2), 
N (7-5), 0,(8-2), U (9-0), Y (9-6) and Z (io-i). The inset 
chart — not inverted this time — shows the trio together with 
Regulus and the fourth-magnitude Omicron Leonis, R Leonis is 
a convenient star, because it never becomes very faint. 



(Naked-eye view) 

Regulus R>N »( 


21 -6-6 

M = 7'2 

N = ?-5 


(Telescopic view) 







U Ononis. A famous red Mira-type variable; magnitude 5-4 to 
12-6; 372 days. Start from Zeta Tauri (page 272) and locate the 
pair of stars Chi 1 and Chi 2 Orionis; from these, identify the 
star 1 1 (magnitude 8 -g) , The second chart (inverted for tele- 
scopic use) shows the field round n. Comparisons: Chi 1 (4-5), 
CM 2 (5-8), 4 (7-2), 5 (7-9), 7 (8-4), 11 (8-9), 14 (9-2), 21 (97), 
29 (9'9) 3 _39 (io-6), 45 (11 -2), 62 (11 -6), 99 (12-3). Beware of 
UW, which is a Beta Lyra eclipsing binary with a range of 
from 10-9 to 1 1-8 and a period of one day. 

U Orionis is awkward inasmuch as its period is only a week 
longer than a year, and at the moment it reaches maximum 
during northern summer (about June/July) when it is too near 
the Sun to be seen. It reaches maximum about a week later 
each year, so that during the 1980s it will be at its brightest 
when well placed, and will be best studied with binoculars. 


•+• P Tauri 


,1 • CTai 

■*^ ■ - ■ 





(Naked-eye view) 




'14 ©u 





(Telescopic view) 


X 1= 4"5 
X s = 5-8 

4 = 7-2 


7 = 8-4 




29 = 9-9 
39 = 10-6 
45 = 1 1 -2 
62 = 11-6 
99 = 12-3 


• • 

• 11 

• 14 O^jOUW 


• 21 


( Telescopic view) 

• • 



I have left until last the baffling variable R Corona, which 
has a range of from 5-8 to about 15. When at maximum — that 
is to say, for most of the time — it is on the fringe of naked-eye 
visibility, and is a binocular object; compare it with M (6-6) or 
1 (7-2). If you look for it with binoculars and cannot find it, 
you may be sure that it has suffered one of its deep, unpredict- 
able falls. If so, you will need a large telescope and a specialist 
set of charts to locate it. 

1 =7-2 


Appendix XXIX 


As I pointed out in Chapter Thirteen, I am not a radio 
astronomer; moreover this book is concerned with visual work, 
and it may even be that I have said too little about photo- 
graphic techniques. On the other hand, radio astronomy is now 
so important that it cannot be ignored. 

The original observations of radio waves from the sky were 
made in the early 1930s by Karl Jansky, who was working on 
an entirely different programme — he was a communications 
engineer — and who never followed up his discoveries as he 
might have been expected to do. A few years later Grote 
Reber, an American amateur, built the first true radio tele- 
scope and undertook researches of pioneer importance. Then 
came the war, during which radio and radar techniques were 
developed to a remarkable degree. After the end of hostilities, 
it seemed as though researches of this kind, including radio 
astronomy, would remain solely in the hands of professional 

As far as really fundamental advances are concerned, this 
is of course true. The cost of equipment even remotely com- 
parable with that at a professional establishment would be far 
beyond the means of the wealthiest amateur, and to set up an 
installation of such a kind would be rather poindess in any case. 
On the other hand, it has now been shown that the serious 
amateur is capable of useful work if he is prepared to spend 
time and a certain amount of money in constructing adequate 
equipment. Oddly enough, the main cost lies in the recording 
devices rather than in the aerials themselves. 

In its simplest form, a radio telescope consists of an aerial 
together with a radio receiver and a recording device. A 
"radiometer" of this sort may be used for the measurement of 
daily changes of intensity of, for example, the radio emissions 
from the Sun, and it may be designed so as to cover several 
frequencies at the same time. If sufficient space is available, 



radiometers or aerial systems may be combined to make an 
"interferometer". Steerable radio telescopes may also be 
constructed. It is obvious that the would-be astronomer must 
have a thorough working knowledge of electronics ; in fact he 
must be an electronics man first and an astronomer afterwards. 

Radio telescopes are of many designs. The "dish", of which 
the greatest example is the 250-foot paraboloid at Jodrell Bank, 
is the best-known, but other instruments do not look like 
telescopes in any sense of the word, and give the general 
impression of a haphazard collection of poles and wires. I do 
not propose to go into details here; this is best left to a radio 
astronomer, and I have listed some useful books on Page 343. 
Meanwhile, it may be worth giving a few notes about the types 
of radio sources to be found in the sky. 

First, of course, there is the Sun, whose radio emissions may 
be studied with amateur equipment. Large-scale disturbances 
may be recorded from the active Sun; with the quiet Sun, the 
slowly-varying component is observable, and flares produce 
very marked effects. There are also more specialised investiga- 
tions. Each year the Sun passes close to the famous Crab 
Nebula in Taurus, the supernova wreck which is itself a 
powerful radio source. The Nebula is occulted by the solar 
corona, and the various effects produced are of great signific- 
ance. Amateurs can do valuable work here, beginning their 
observations in mid-May and continuing until mid-July. 

Jupiter is another radio source of interest to the well-equipped 
amateur. Of course, most sources lie not only beyond our Solar 
System, but also beyond our Galaxy; and the serious radio 
astronomer is above all a specialist in electronics. By all means 
build a radio telescope if you feel so inclined — but be sure to do 
some very serious reading before starting out! 


Appendix XXX 


Powerful astronomical telescopes are stricdy non-portable, 
and some sort of observatory is highly desirable. For the reasons 
given in the text— and which are in any case obvious— a dome 
is ideal, but it is not easy to make and is prohibitively expensive 
to buy. However, many amateur domes exist. The design which 
I would not favour is that in which the entire dome revolves; 
there is so much mass to be moved that jamming is inevitable. 
A dome of this sort is shown in Plate II. It was used by the well- 
known Devon amateur Hedley Robinson. He found that it was 
not entirely satisfactory, and has now replaced it with a dome 
in which only the top part revolves. 

The trouble arises from the need for a circular rail. It can be 
made; but it is not easy, and this is not the place to go into 
details. There is an instructive article about it in the 1971 
Yearbook of Astronomy. 

Run-off sheds are much easier, and in general are perfectly 
satisfactory. My own (also shown in Plate II) is made in two 
sections. Each runs back on rails which are concreted in (angle- 
iron will suffice if need be). The shed itself is of wood, but hard- 
board is satisfactory enough. If the shed is made in one piece, 
one has to have a door at one end, and this, in my view, is not 
a good idea. If hinged, it will flap awkwardly; and to remove it 
entirely is not easy when one is working in the middle of the 
night and one's hands are cold. Moreover, any sort of door may 
tend to act as a powerful sail in a high wind. The construction 
of a two-piece run-off shed is a sheer problem in carpentry, and 
the photograph should give adequate guidance. 

Another method is to have an observatory in which the roof 
is run back on rails — the ends of the rails being supported, 
either as shown in the upper right photograph in Plate II, or by 
being fixed to the tops of poles concreted into the ground. If 

* 337 


this pattern is adopted it is wise to make the roof as light as 
possible; plastic will suffice. The run-off roof idea is best suited 
for refractors, which have to be higher than reflectors and for 
which a run-off shed would need to be inconveniently tall. 
Remember, wind-force is a factor to be borne in mind. 

Great care should be taken in the choice of a site for an 
observatory. According to the principle of Spode's Law ("If 
things can be awkward, they are"), trees and houses are always 
in the most inconvenient possible positions. If you can, select a 
site which is not only away from obstructions, but also well 
away from artificial lights, and from houses — which will give 
out warmth, so ruining definition. Above all, never put an 
observatory on top of a dwelling-house; flat roofs may look 
tempting, but are to be avoided, A rooftop observatory has the 
worst of all possible worlds. It will experience the full force of 
the wind, and there will be so much warmth rising that no useful 
work will be possible. 

Inevitably, the available sites will be far from ideal; and it is a 
question of making the best of things. For instance: if you are 
interested chiefly in the Moon and planets, select the site with 
the most favourable southern horizon. Inconvenient artificial 
lights can sometimes be screened. Even in my home in Selsey, 
within sound of the sea on the Sussex coast, I have had to put a 
screen in my garden to shield one awkward street-lamp. 
Reluctantly, I rejected the idea of using an air-gun to extin- 
guish it permanently! 

Appendix XXXI 



Any amateur who wants to take a real interest in astronomy 
will be well advised to join a society. The advantages of doing so 
are obvious. The enthusiast will be able to collaborate with 
others, and to exchange information and points of view. 
Incidentally, he will make many friends. 

In Britain, the leading organization for amateurs is the 
British Astronomical Association, which was founded in 1890 
and has an observational record second to none. The secretarial 
address, from which all information may be obtained, is: 
British Astronomical Association, Burlington House, Piccadilly, 
London W. 1 . No qualifications other than patience and enthu- 
siasm are needed for entry, and there is no age limit. Monthly 
meetings are held at 23 Savile Row, on the last Wednesday of 
each month at 5 p.m. {October-June inclusive) ; there is also an 
annual Away Meeting— for instance, that of 1 970 was at Tor- 
quay. There is a regular Journal, and there are a number of 
other publications. Moreover, there are various sections, each 
of which is in charge of an experienced Director and which 
members may join if they so wish. 

There are also many local societies, many of which are very 
well-equipped. A full list is published annually in die Yearbook 
of Astronomy; few large cities are without them. To mention only 
a few, there are flourishing societies in Birmingham, Liverpool, 
Chesterfield, Norwich, Edinburgh, Glasgow, Leeds and the 
Torbay area. In Ireland there is the Irish Astronomical Society, 
with centres in Belfast, Dublin, Armagh and Londonderry. The 
chief secretarial address is 1 Garville Road, Dublin 6; in 
Northern Ireland, full information can be obtained from The 
Planetarium, Armagh. 

Amateur societies also flourish in many other countries. In 
the United States, a list is given annually in the American 
edition of the Yearbook of Astronomy, published by W. W. Norton 


& Co. Inc. There are many amateurs in the Astronomical 
Society of the Pacific (675 18th Avenue, San Francisco 21, 
California) and in the American Association of Variable Star 
Observers, which also has a solar section. Amateurs also belong 
to the Royal Astronomical Society of Canada, which has 
various Centres. 

In the southern hemisphere, there are the Royal Astro- 
nomical Society of New Zealand, the South African Astro- 
nomical Society, and many societies in Australia, 

I have dealt here only with English-speaking countries, and 
the list I have given is the barest of outlines; but information is 
not hard to obtain. Note, too, that amateurs are by no means 
excluded from some of the eminent professional organizations, 
such as Britain's Royal Astronomical Society. Indeed, the list 
of Past Presidents of the Royal Astronomical Society includes 
the names of several amateurs, though this is naturally very 
much the exception to the general rule. 


Appendix XXXII 


Astronomical literature is so vast that it is quite out of the 
question to give more than a very brief selection. Emphasis here 
has been laid on popular and semi-popular works; those which 
are slightly more technical are distinguished by an asterisk. 
There are, of course, many periodicals, notably Sky & Telescope, 
published by the Sky Publishing Corporation, Cambridge 
02138, Mass., U.S.A. This appears monthly, and is easy to 
obtain in Britain. Of course there are society journals, notably 
that of the British Astronomical Association. 


Yearbook of Astronomy. Sidgwick & Jackson, annually. 


abell, g. Exploration of the Universe: Brief Edition, Holt, Reinhart 

& Watson, 1969. 
ASIMOV, i. Asimov on Astronomy. Hutchinson, 1 974. 
baker, r. and fredrik, l. Astronomy. Van Nostrand, 1971. 
kienle, h. * Modern Astronomy: an Introduction. Faber & Faber, 

mitton, s. (editor), Cambridge Encyclopedia of Astronomy. 

Cambridge, 1977. 
Moore, Patrick. Atlas of the Universe. Mitchell Beazley, 1978. 
moore, Patrick. The A~Z of Astronomy. Fontana Paperbacks, 


NIC olson, i. Astronomy : a Dictionary of Space and the Universe. 
Arrow Books, 1977. 

payne-gaposchkin, c. Introduction to Astronomy. Eyre & Spottis- 
woode, 1956. 

Pickering, J. s. 1 00 1 Questions Answered about Astronomy. Lutter- 
worth, 1975. 


abetti, g. The Sun. Faber & Faber, 1962, 
Baxter, w. m. The Sun and the Amateur Astronomer. David & 
Charles, 1973. 




Baldwin, r. b. * The Measure of the Moon. Chicago Press, 1963. 
fielder, o. * Lunar Geology. Lutterworth, 1 965. 
French, b. m. The Moon Book. Penguin, 1977. 
moore, Patrick. Guide to the Moon. Lutterworth, 1976. 
Moore, Patrick. {Lunar Map) Map of the Moon (2 ft). Tun- 
bridge Wells, 1970. 
taylor, s. r. Lunar Science : a Post-Apollo View. Pergamon, 1 975. 


(Mercury and Venus) 


burgess, e. and Murray, b. Flight to Mercury. Columbia Press, 


cross, c. A., and moore, Patrick. Atlas of Mercury. Mitchell 
Beazley, 1977. 


moore, Patrick. Guide to Mars. Lutterworth, 1977. 


peek, b. m. The Planet Jupiter. Faber & Faber, 1963. 


Alexander, a. f. o'd. The Planet Saturn. Faber & Faber, 1962. 


Alexander, A. F. o'd. The Planet Uranus. Faber & Faber, 1964. 

(Minor Bodies) 

burns, j. a. (Ed.) Planetary Satellites. University of Arizona Press, 

roth, d. d. The System of Minor Planets. Faber & Faber, 1962. 


baum, r. m. The Planets: Some Myths and Realities. David & 

CharleSj 1973. 
moore, Patrick. Guide to the Planets. Lutterworth, 1976. 
Whipple, f. l. Earth, Moon and Planets. Oxford, 1 976. 




harang, l. *The Aurora. Chapman & Hall, 1952. 

ST0RMER, c * The Polar Aurora. Oxford (Clarendon Press), 1955. 


brown, p. l. Comets, Meteorites and Man. Hale, 1973. 
mccall, G. j. h. Meteorites and their Origins. David & Charles, 

moore, Patrick. Guide to Comets. Lutterworth, 1977. 

nininger, h. h. Out of the Sky. Constable, 1959. 

richter, N. The Mature of Comets. Methuen, 1963. 


hey, j. s. The Radio Universe. Pergamon, 1971. 
hey, j. s. The Evolution of Radio Astronomy. Elek, 1973. 
LOVELL, sir Bernard. * Tke Story of Jodrell Bank. Oxford,! 971. 
lovell, sir Bernard. *Out of the Z m ^ n - Oxford, 1973. 


abetti, g., and hack, m. Nebuhe and Galaxies. Faber & Faber, 

asimov, 1. The Collapsing Universe. Hutchinson, 1977. 
baade, w. The Evolution of Stars and Galaxies. MIT Press, 1975. 
glasby, j. s. Variable Stars. Constable, 1968. 
moore, Patrick. Guide to the Stars. Lutterworth, 1974. 
nicolson, 1. and moore, p. Black Holes in Space. Orbach & 

Chambers, 1975. 


Norton, a. p. Star Atlas and Telescopic Handbook. Gall & Inglis, 

I 973- 
(This book has run to many editions. I regard it as indispens- 




roth, g. d. Handbook for Planet Observers. Faber & Faber, 1970, 

Various. * Practical Amateur Astronomy. Lutterworth, 1975. 


Howard, n. Handbook of Telescope Making. Faber & Faber, 1962. 
ingalls, a. (ed.) * Amateur Telescope Making. Scientific American, 

last volume issued in 1953. 
Various. Astronomical Telescopes and Observatories for Amateurs. 

David & Charles, 1973. 


armttage, a. John Kepler. Faber & Faber, 1966. 

Collins, p. and moore, p. The Astronomy of Southern Africa. 

Howard Timmins (Gape Town) and Hale (London), 1976. 
dreyer, j. History of Astronomy from Thales to Kepler. Dover 

Books, 1952. 
moore, Patrick. The Story of Astronomy, Macdonald, 1977. 
shapley, h. and howarth, H.E. Source Book of Astronomy. 

(Period before 1900.) McGraw Hill, 1929 
shapley, h. Source Book of Astronomy. (Period 1900-50.) 

McGraw-Hill, i960. 
ronan, c .a. Edmond H 'alley. Doubleday, 1969, 
Whitney, c. a. The Discovery of our Galaxy. Knopf, 197 1. 
wright, h. Explorer of the Universe (G. E. Hale). Dutton 1966. 


alfv£n, h. Worlds- Antiworlds. W. H. Freeman, 1966. 
allen, d. a. Infrared: the Mew Astronomy. David & Charles, 1975. 
de vaucouleurs, g. Astronomical Photography. Faber & Faber, 



king-hele, d. * Observing Earth Satellites, Macmillan, 1966. 
shkxqvskii, 1. s. and sagan, c. Intelligent Life in the Universe. 
Holden-Day, 1966. 

moore, Patrick. Astronomy for c O' Level. Duckworth, 1973. 



A-stars, 164 

AD Leonis, 323 

Achemar, 274, 301 

Acidalium, Mare, I 1 6 

Acrux, 305 

Adams, J. G., 133-4 

Aerolites, 152 

Agatharchides A (lunar crater), 337 

Airglow, 10a 

Airy, SirG., 133 

Albategnius (lunar crater), 331 

Albireo, 173, 387 

Akoct, G. E. D., 152, 189, 190 

Alcor, 1 76, 269 

Aldebaran, 374 

occultations of, 88 
Aldiin, E., 75, 80 
Alexandria, library at, 20, as 
Algol, 179-80, 181, 383 
Alhena, 188 
Alkaid, 158 
Almagest, the, 21, 23 
Alnitak, 271 
Alniiam, 271 

Alphabet, Greek, 157, 253 
Alpha Centauri, 30, 157, 30 1, 306 
Alpha Herculis, 184, 392-3 
Alphard, 367, 378 

Afphonsus (lunar crater), 85, 235, 238 
Alpine Valley (lunar), 228 
Alps, lunar, 76, 228 
Altai Mountains (lunar), 231 
Altair, 157, 286, 288 
Altazimuth mount, see Mountings, 

Alirminizing, 45 
Amalthea, 127 
Amateur astronomy, opportunities for, 

Ananke, 127 

Anaxagoras {lunar crater), 234 
Anaximenes (lunar crater), 234 
Andromeda, 283, 285, Map VII 

Great Spiral in, 31, 200, 285 
Antares, 165, 174, 291, 295,301 

occupations of, 88 
Antlia, 312, Map XIV 
Antoniadi, E. M., 117 
Apennines, lunar, 76, 233-4 
Apollo programme, 74-5, 80- 1, 193, 

Apus, 313, Map XV 
Aquarius, 288, 297, Maps VIII, X 
Aquila, 288-9, Map VIII 

Ara, 308, Map XIII 

Arabs, the, 22 

Arago (lunar crater), 229 

Archimedes (lunar crater), 234 

Archytas (lunar crater), 229 

Arcturus, 157, 165, 266, 29!, 301 

Argo Navis, 277, Maps V, XIV 

Ariadsus Cleft, 339 

Ariel, 133 

Aries, 51, 296-7, Map X 

First Point of, 52, 155-6, 297 
Aristarchus (lunar crater), 82, 86, 234 
Aristillus (lunar crater) , 229 
Aristoteies (lunar crater), 229 
Aristotle, 20, 21, 23 
Armagh Observatory, 86, 130 
Armstrong, N., 75, 80 
Arrhenius, S., 114 

Artificial satellites, see Satellites, arti- 
Arzachel (lunar crater), 238 
Ashen Light, 1 1 1 
Assouan, 21 

Asteroids, see Minor Planets 
Astrology, 22 

Astronomical Unit, 32, 54, 122 
Astronomy, history of, 17-33 

uses of, 14-16 
Atlas (lunar crater), 229 
Atmosphere, unsteadiness of, 47-6 
Auriga, 274-5, Map ^V 
Aurora, 34, 68, 99-xot, 103 

cause of, 100 

displays of, 101 

methods of observing, 100-1 

on Venus?, Ill 
Australe, Mare, 231 
Australia, sky from, 300-19 
Awtolycus (lunar crater), 229 
Autumnal Equinox, see Libra, First 
Point of 

B-stars, 164, 166 
Bacon, Roger, 25 
Barnard's Star, 168 
Barrow, G. H., 310 
Barycentre, the, 74 
Baxter, W. M., 72 
Bailly (lunar crater), 236 
Barwell Meteorite, 152-3 
Bayer, star-catalogue of, 156-7 
Bean, A., 80 
Becquerel, 13 



Beer {lunar crater), 324 
Bcllatrix, 367, 271 
Bessel, F. W., 30, ?59 
Bessel (lunar crater), as8 
Beta Lyra:, 180, 286-7 
Betelgeux, 160, 165, 179, 27"i 373 
Billy (lunar crater), 236 
Binary stars, 171-2 
eclipsing, 178-81 
Binoculars, 25, 34, 49, 324-7 
Birt (lunar crater), 236 
Bode, J., 130 
Bondi, H., 205 

Bootes, 281, 391-3, Maps VI, IX 
Boscovitch (lunar crater), 239 
Bovedy Meteorite, t53 
Brinton, H,, go 
British Astronomical Association, 96, 


Artificial Satellite Section, 223 

Aurora Section, 101 

Handbook of, 67, 89, 1 16, 121, 126, 145 

Jupiter Section, 14, 124 

Lunar Section, 85-6 

Meteor Section, 149 
Bullialdus (lunar crater), 236 
Burg (lunar crater), 329 
Burke, B. F., 136 

Cailum, 373, 301, Maps IV, XI 
Callisto, 126-7 
Caloris Basin, 106 
Gamelopardus, 271, Map III 
Campanus (lunar crater), 237 
Cancer, 275, 278, Map V 
Ganea Venatici, 281, Map VI 
Canis Major, 275, Map V 
Ganis Minor, 375, Map V 
Ganopus, 20, 156, 157, 160, 164, 169, 
277, 30 !, Map XI 1, 309, Map XIV 
Gapella, 156,266,267 
Gapella (lunar crater), 331 
Capricornus, 289, 291, Map VIII 
Carina, 185, 309, Map XIV 
Car me, 127 

Carpathian Mountains (lunar), 234 
Carrington, J., 69 
Cassini (lunar crater), 330 
Cassini Division, 139 
Cassiopeia, 265, 282, Map VII 
Cassiopeia A, 3 1 1 
Castor, 176, 188, 265, 277 
Catharina (lunar crater), 233 
Caucasus Mountains (lunar), 76, 228 
Centaurus, 306, Map XIII 
Cepheid Variables, see Variable Stars 
Cephcus, 271, 282-3, Map VII 
Ceres, lao 

Getus, 274, 297, Maps IV, X 
Chaldaeans, 18, 51 

Chaitwcleon, 313, Map XV 

Cheops, Pyramid, of, 18 

Chinese, the, 18-ig, 65 

Chiron, 121 

Chromosphere, the, 64-5 95, 97 

Circinus, 306, Map XIII 

Glavius (lunar crater), 336 

Cleomedes (lunar crater), 230 

Clock drives, 41—2 

Clouds of Magellan, see Nubecula; 

Clusters, star, 191— 4 

globular, 192-3 

in Hercules, 193, 393 

open, 192 
Goal Sack, the, 196 
Columba, 273, Map IV 
Coma Berenices, 281, Map VI 
Comets, 19,59-60, 137-48 

appearance of, 137 

Arend-Roland, 143 

Bennett's 144 

Biela, 147-8 

Brorsen, 147 

Bumham, 144 

coma, 137-8 

Grommelin, 142 

Daylight, 144 

Don at i, 143 

Encke, 139, 14a, 145 

Giacobini-Zinner, 150 

great, 143 

Hallcy, 5Ch&>, 139-41, 142, 148 

Ikeya-Seki, 144 

Kohoutek's, 144 

lost) 146-7 

nature of, 59, 137-8 

nomenclature, 142 

periodical, 139 

periodical, list of, 239 

Quenisset, 142 

Schwassmann-Wachmann I, 141 

searching for, 145-6 

tails of, 137-8 

West's, 144 
Conrad, C. 80 
Constellations, 264-308 

circumpolar, 155 

list of, 241-3 

names of, 154 

obsolete, 154 

Ptolemy's list of, 154 

Zodiacal, 51 
Continuous creation, stt Steady-state 

Copernicus, Nicolas, 23-4 
Copernicus (lunar crater), 79, 334 
Cordillera Mountains (lunar), 235 
Corona, the (solar), 65, 95—7 
Corona, auroral, 101 
Corona Australis, 308, Map XIII 



Corona Borealis, 291-2, Map IX 

Gorvan, P. G., 130 

Gorvus, 281, Map VI, 301 

Gounterglow, see Gcgenschein 

Crab Nebula, 169, 189, 196, 336 

Crater (constellation), 381, Map VI 

Craters, lunar, set Moon 

Crepe Ring, 139, 131 

Crisium, Mare, 76, 84, 228 

Criiger (lunar crater), 236, 238 

Crux Australis, 154-5, 300-2 > 305, 

Guvier (lunar crater), 232 
Cygnus, 287, Map VIII 
Cygnus A, 303 
Gyrillus (lunar crater), 333 

D'Alembert Mountains (lunar), 335 

Dark nebula;, set Nebula: 

D' Arrest, H., 133 

Decimation, 41, 155-6 

Deimos, 1 18-19 

Delphinus, 288, Map VIII 

Delta Cephei, 178, 181, 183, 383 

Deneb, 169, 286, 287 

Denning, W. F,, 117, 151 

Dew-caps, 45 

Dewhirst, D. W., 144 

Dionc, 131 

Dionysius (lunar crater),230 

Diphda, 267, 297 

Doppelmayer (lunar crater), 336 

Doppler Effect, 161-2, 175 

Dorado, 314, Map XV 

Diirfcl Mountains (lunar), 235 

Double Stars, 170-7, 255 

coloured, 173-4 

measuring, 173 

position angles, 173 

"test", 357 
Draco, 269-71 , Map III 
Dubhe, 160 

Dumb-bell Nebula, 288 
Dusky Ring, stt Crepe Ring 

EU Delphini, 325 
Earth, the, 17, 30, 49-51 

according to the Greeks, 19-22 

age of, 204 

circumference, measured by Eratos- 
thenes, 20—1 

fate of, 206-7 

velocity in orbit, 54 
Echo satellites, 233 
Eclipses, 19 

lunar, 20, 55, 90-3, 220 

solar, 93-8, 221 

total solar, of 1954, 96-7 

total solar, of 1961, 97-8 
Ecliptic, the, 51 

Egyptians, the, 18-9 

Elara, 127 

Elements, the, 63-4 

Ellipse, method of drawing, 34 

Enceladus, 131 

Encke's Division, 139 

Endymion (lunar crater), 230 

Epicycles, 31 

Epsilon Auriga:, 167, 168, 180, 275 

Epsilon Lyra;, 176, 286 

Equator, celestial, 51 

Equatorial mounting, see Mountings, 

Equuleus, 288, Map VIII 
Eratosthenes, 20- 1 

Eratosthenes (lunar crater), 77-8, 234 
Eridanus, 273-4, 3'4» Maps IV, XI, 

Eros, 121-3 
Eta Argus, 185, 307 
Euclides (lunar crater), 336 
Eudoxus (lunar crater), 230 
Europa, 136-7 
Everest, Mount, 75 
Extinction, 187, 258 
Eyepieces, 25, 35, 46 

F-stars, 164 

Fabricius, D., 183 

Fabricius (lunar crater), 233 

Faculae, 63, 68, 72 

False Gross, 301, 309 

Field, telescopic, size of, 356 

Finders, 44-5 

Firminicus (lunar crater), 230 

First Point of Aries, stt Aries, First 

Point of 
Flagstaff Observatory, see Observatory, 

Flamsteed, J., 37, 48, 157 
Flamsteed House, 38 
Flares, solar, 69 
Flare stars, 190, 322 
Flocculi, 65 
Focal length, 36 
Focal ratio, 36 

Feecunditatis, Mare, 228, 231 
Fomalhaut, 299 
Fornax, 274, Map TV 
Fox, W. E., 123 

Fractional method (variable stars), 187 
Fra Mauro (lunar crater), 81, 236 
Franklin, K. L., 136 
Fraunhofer, J., 29, 63 
Fraunhofer Lines, 63-4 
Frigoris, Mare, 228, 233 

G-stars, 164 
Gagarin, Y., 33 



Galaxies, 199-202 

colliding, obsolete theory of, 20a 

status of', 31, 200 
Galileo, 26, 76, 197 
Galle,J., 133 
Gamma Argus, 164 
Gamma Cassiopeia, 181 , 185, 282 
Gamma Virgins, 176, 280 
Ganymede, 126-7 
Garstang, R. H., 263 
Gassendi (lunar crater), 85, 234-7 
Gauss (lunar crater), 230 
Gcgenschein, the, 102 
Gemini, 277-8, Map V 
Gcminus (lunar crater), 230 
George III, 28 
Gingerich, O., 263 

Globular clusters, see Clusters, globular 
Goclenius (lunar crater), 232 
Godin (lunar crater) , 230 
Gold, T., 205 
Granulation, solar, 69 
Great Bear, see Ursa Major 
Great Red Spot, see Jupiter 
Greek alphabet, ste Alphabet, Greek 
Grimaldi (lunar crater), 93, 237 
Grossie, H. H. R., 144 
Gruithuisen, F, von P., 1 1 1 
Grus, 318, Map XVT 
Gutenberg (lunar crater), 232 

HR Delphini, 189-90, 322, 325 

Hsdi, the, 275 

Hxmus Mountains (lunar), 228 

Haise, F., 81 

Hale, G. E, s 47 

Halley, Edmond, 48, 59, 139 

Halley's Comet, see Comets 

Harriott, T., 76 

Hatfield, H., 87 

Hay, W. T., 13, 128 

Hedley Robinson, J., 337 

Helium, 15, 164, 166-7, '95 

Hellas (Martian), 1 15 

Henderson, T., 30 

Heraclitus (lunar crater), 232 

Hercules (constellation), 2gi, 292-3, 

Maps VIII, IX 
Hercules (lunar crater), 230 
Hercynian Mountains (lunar), 234 
Hermes, 122 
Herschel, Sir J., 29 
Herschcl, Sir W., 28-9, 31, 131, 170, 

194 „ 
Hesiodus (lunar raster), 237 
Hidalgo, 121 
Htmalia, 137 

Hippalus (lunar crater), 237 
Hippaxchus, 22 

Hipparcbus (lunar crater), 232 

Hodgson, 69 

Hole, G. A., 175 

Honda, 190 

Horologium, 314-15, Map XV 

Horoscopes, 22 

Horse's Head Nebula, see Orion, 

Nebula in 
Hoyle, F., 205 
Hsi and Ho, 19 
Huggins, Sir W,, 31, 194 
Humboldtianum, Maie, 229 
Humorum, Mare, 235 
Hussey.T.J., 133 
Huygens, C, 27, 128 
Hyades, the, 192, 274 
Hyginus Cleft, 79, 229 
Hydra, 278, 281, Maps V, VI, IX 
Hydrogen, 63, 65, 166, 164-7, 195 
Hydrus, 3 14, Map XV 
Hyperion, 131 

Iapetus, 131 

Icarus, 122 

Imbrium, Marc, 76-7, 233 

Indus, 317, Map XVI 

International Geophysical Year, 67 

International Year of the Quiet Sun, 67 

lo, 126-7 

Iridum, Sinus, 234 

Iron, spectrum of, 63 

Isidorus (lunar crater), 231 

Jansky, K, 32, 335 

Janssen (lunar crater), 232 

Janus, 131 

Jodrcli Bank, 32, i6g, 190, 336 

Julius Caesar (lunar crater), 230 

Jupiter, 17, 21, 50, 52, 58-9, 132-8 

belts on, 123 

brilliance of, 132 

comet family of, 139 

cons titu don of, 122-3 

dimensions and mass of, 122 

Great Red Spot on, 123-4 

methods of observing, 124-6,317-8 

oppositions of, 216 

radio waves from, 14, 126, 336 

satellites of, 26, 28, 42, 59, [36-8 

South Tropical Disturbance on, 124 

spots on, 133 

temperature of, 123 

transits of surface features, 125-6, 
Jura Mountains (lunar), 234 

K-itars, 164-5 
Kepler, J., 24-5, 26,52 



Kepler's Laws, 25, 52-4 

Kepler (lunar crater), 234 
Klein (lunar crater), 231 
Kocab, 265, 369 
Kozyrev, N., 85, 235 
Kuiper's Star, 167-8 
Kukarkin, catalogue of variable stars 
by, 179 

Lacerta, 283, Map VII 
Lagoon Nebula, 289 
Landsberg (lunar crater), 80 
Led a, 127 

Langrenus (lunar crater), 232 
Lemaitre, Abb*, 304 
Lens-making, 37 
Leo, 279, Map VI, 300, 301 
Leo Minor, 279, Map VI 
Lepus, 273, Map IV 
Lctronne (iunar crater), 237 
Le Verrier, U. J, J„ 133-4 
Libra, 293, Map IX 

First Point of, 155 
Librations, lunar, 76 
Licetus (lunar crater), 232 
Light, velocity of, 28, 30 

wave nature of, 35 
Limb, lunar, 76-7 
Linn* (lunar formation), 85, 93, 328 
Lippersheim, H., 25 
Local Group of galaxies, 301 
Lovell, J., 81 
Lowell, P., 114, 116, 134 
Luna 9, 80 
Luna 17, 81 
Lunik III, 79 
Lunokhod i & 2, 81 
Lupus, 307, Map XIH 
Lyra, 284-7, Map VIII 
Lynx, 285, Map VII 
Lyot filter, see Monochromatic filter 
Lysithea, 127 

M-stars, 164-5 

Macrobius (lunar crater), 230 
Magellanic Clouds, see Nubecula: 
Maginus (lunar crater), 337 
Magnetic storms, 100 
Magnification . 36, 46 
Magnitudes, stellar, see Stars, magni- 
tudes of 
Manilius (lunar crater), 230 
Margin is, Mare, 2sg 
Mariner 2, 109 
Mariner 4, 61, 115, 1 18-19 
Mariner 5, tog 
Mariner 6, 115, 117 
Mariner 7, 115, 117 
Mariner 9, 11 5- 16 

Mariner 10, 106, 1 09 
Mars, 50, 51, 52, 61, go, 104, 112-19, 
atmosphere of, 114, 1 15-16, 119 
canals of, 1 13-1 4, 1 1 5-16, 1 1 7 
caps, polar, 1 1 3—t 5 
clouds, 1 16 

craters on, 33, 114-15, 1 19 
dark areas, 1 14-15 
deserts, 114, 115 
dust storms, 115 
map of, 214-15 
methods of observing, 1 16-18 
movements of, 57-8 
oppositions of, 1 12-13, 316 
phases of, 112 

probes to, 61, 114-16, 118-19 
satellites of, 1 18-19 
temperature on, 1 14 
vegetation on?, 114-15 
vulcanism on, 115-16 
Marsden, B,, 127 
Maurolycus (lunar crater), 232 
McLaughlin, D. B,, 1 14 
Measure, angular, 356 
Mcchain, M., 363 
Megrez, 187-8 
Menelaus (lunar crater), 330 
Mcnsa, 313, Map XV 
Merak, 160 

Mereator (lunar crater), 237 
Mercury, 1 7, 21, 50-2, 53-4, 90, 104-8, 
atmosphere of, 106 
elongations of, 212 
identifying, 53 
magnetic field, 106 
map of, 105, 106 
methods of observing, 107 
phases of, 55, 57 
rotation of, 105-6 
surface markings on, 106-7 
temperatures on, 105-6 
transits of, 107--8, 212 
Meridian, 156 

Mersenius (lunar crater), 237 
Messier, C, catalogue of nebulae and 

clusters, 146, 192, 260-3 
Messier (lunar crater), 232 
Meteorites, 152-3 
Meteors, 60, 137, 148-53 
Aquarids, 148 

connection with comets, 148 
Giacobinids, 150 
Leonids, 149-50 
methods of observing, 150-1 
micro-, 148 
Orionids, 149 
Perseids, 149 
possible lunar, 93 

35 1 


Meteors — cont. 

Quad ran tids, 154 

radar detection of, 151 

radiants, 149 

shower, 148-50 

showers, list of, 240 

sizes of, 148 

sporadic, 148 

velocities of, [48 
Melius (lunar crater), 332 
Micrometers, 173 
Microseopium, 318, Map XVI 
Middlehurst, Barbara, 86 
Milky Way, the, a6, 31, 42, 107, 199 
Mimas, 131 
Minor Planets, 51, 59, iao-2 

Earth-grazing, 131-3 

identifying, 121 

number of, 120 

sizes of, 1 30 

tables of, an 

Trojan, 121 
Mintaka, 271 

Mira, 165, 183-4, ^74. ^97, 3^7 
Miranda, 133 
Mirror-grinding, 39-40 
Mitchell, T„ 81 
Mizar, 170, 176, 269 
Moltke (lunar crater), 80 
Monoceios, 377, Map V 
Monochromatic filters, 65, 72 
Montanari, G., 179 

Moon, the, 14, 17, 21, 22, 26, 31, 54, 
61, 73-87 

age, 7+ 

apparent size of, 88 

atmosphere of, 74 

clefts, 78-g 

craters, 77-8 

crater depths, 77 

crater origin, 78 

dimensions and mass of, 74 

distance of, 73 

domes, 79 

eclipses, set Eclipses, lunar 

hidden side of, 76 

"hot spots" on, 93 

limiting detail with various apertures, 

maps of, 82-4 

methods of observing, 82-4 

mountains, 34, 76-7 

observations by Schroter, 39 

phases of, 54-5 

probes to, 74, 78-81 

rays, 79 

rotation of, 75-6 

samples from, 76, 79, 8t 

seas, 76-7 

surface features on, 76-9, 80-1 

variations on, 85-7 
Moonquakes, 83, 86 
Moon-Blink device, 86-7 
Moretus (lunar crater), 237 
Moseley, T, J, G. A., 86, 124, 130 
Mountings, telescopic, 40-3 

altazimuth, 40 

equatorial, 41-3 

pillar and claw, 40-a 
Mu Gephei, 184, 383 
Multiple stars, 176 
Musca Aus trails, 313, Map XV 

N-stars, 164-5 
Navigation, 15 
Nebulas, 39, 31, 194-6 

catalogue by Messier, set Messier 
catalogue of nebulas 

Crab, set Crab Nebula 

dark, 195-6 

gaseous, 194-6 

in Orion, set Orion, Nebula in 

methods of observing, 1 96 

planetary, 194-5 

spectra of, 31, 194 
Nebulium, ig5 
Ncctaris, Mare, 331 
Neptune, 90, 133-4 
Nereid, 134 
Neutron stars, 169 
New Zealand, sky from, 300- ig 
Newton, Sir Isaac, 26-7, 35, 63 
Newtonian reflector, see Telescopes, 

reflecting, Newtonian 
Nodes, the, 92 
Norma, 306, Map XIII 
Norton's Star Atlas, 268, 343 
Novae, 188-9, 3 3S 

Aquilsc, 186 

cause of, 188 

Ddphini, 189-90, 332, 325 

He re ul is, 189, 391, 393 

methods of observing, 189 

list of, 359 

Peisei, 188 

Scud, 190 

Vulpecufas, 190 
Nubecula:, 199, 313-14, 315 
Nubium, Marc, 235 

O -stars, 164 
Oberon, 133 

Object-glasses, cleaning, 45 

compound, 35 
Observatory, 47 

amateur, construction of, 337-8 

ancient, 33 

Armagh, 86, 130 

Copenhagen, 27 



domed, 47 

educational, 34 

Greenwich, 15, 27, 32, 48 

Herstmonceux (Greenwich), 32, 48 

Leyden, 27 

Lick, 47 

Lowell, 49, 144 

Mcudon, 48 

Mount Wilson, 31, 48 

Palomar, 31, 47 

Paris, 27 

Pic du Midi, 48-9 

Preston, 34 

run-off, 47, 49 

Siding Spring, 32 

Uraniborg (Tycho'sl. 24 

Yerkes, 48 
Observing from indoors, 46-7 
Occultations, by Moon, 88-go 

by planets, 90 
Octagon Room, 48 
Octans, 313, Map XV 
Officina Typographica, 154 
Olbers (lunar crater), 334 
Olympus Mons (Martian), 1 15 
Omega Ccntauri, 194 
Omega Nebula, 289 
Omar, Caliph, 33 

Ophiuchui, 393, 308, Maps IX, XIII 
Orbiter vehicles, 78, 80-1, 232, 235 
Orientale, Mare (lunar), 335 
Orion, 154, 367-B, 371, Map IV, 304, 
Map XII 

Nebula in, 194-5, *9$i 373 
Owl Nebula, 269 

P Cygni, 322 

Palitzsch (lunar crater), 232 

Pallas, 120 

Palomar, reflector, 32, 47, 163 

Parallax, stellar, see Stars, parallax of 

Pasiphae, 127 

Paton,J., 100 

Pavo, 316, 317, Map XVI 

Pegasus, 388, 396, Maps VIII, X 

Percy Mountains (lunar), 335 

Period-Luminosity Law, Ccpheid, 182- 

„ 3 

Perseus, 1 79, 283, Map VII 

double clusters in, 191-2, 283 
Petavius (lunar crater), 79, 332 
Phillips, T. E. R., 123 
Philolaus (lunar crater), 234 
Phobos, 118-19 
Phosbe, 131, 140 
Pbcenbc, 316, 318, Map XVI 
Photography, astronomical, 31 

auroral, 101 

lunar, 87 

Photometers, 157 

Photosphere, the, 64-5 

Piazzi, G,, 120 

Piccolomini (lunar crater) 332 

Pickering, E. G, 163 

Pickering, W, H., 134 

Pickering (lunar crater), 332 

Pico (lunar mountain), 235 

Pictor, 314, Map XV 

Pillar and Claw mount, see Mounting, 

pillar and claw 
Pioneers 10 & 11, 61, 136 
Pisces, 52, 156, 297, Map X 
Piscis Austrinus, 397, 399, Map X 
Pitatus (lunar crater), 337 
Piton (lunar mountain), 235 
Planetary nebulas, stt Nebulas, plane- 
Planets, 17, 50-9, 104 

beyond Pluto, possible, 135 

extra-solar, 168 

finding in daylight, 156 

how to recognize, 53 

movements of, 57 rf, 

nature of, 51, 58 

orbits of, 51-2 

origin of, 205 

satellites of, 58-9 

tables of, 209 

twinkling of, 57 
Plato {lunar crater}, 77, 8a, 93, 334-5 
Pleiades, 191-3, 374 
Plinius (lunar crater), 228 
Pluto, 50, 58, 134-5 

occulta tions by, 90 
Fogson's Step Method, see step Method, 

Polaris, 155, 157, 158, 161, 265, 269 
Poles, celestial, 155-6 
Pollux, 265, 277 
Populations, stellar, 198-9 
Posidonius {lunar crater), 331 
Prassepe, 191, 193, 378 
Prentice, J. P. M., 13, 188 
Prindpia, the, 26 
Procellarum, Oceanus, 333, 335 
Prod us (lunar crater), 231 
Procyon, 267, 375 
Prominences, 65, 69, 95-6 
Proper motions, stellar, stt Stars, 

proper motions of 
Froxima Centaur i, 159 
Ptolemasus (lunar crater), 82, 238 
Ptolemaic System, 31-3, 36, 38 
Ptolemy, 19, 188, 379 
Pulsars, 167, 169 
"Pup", see Sirius, Companion of 
Puppis, 277, 310, Maps V, XIV 
Purbach (lunar crater), 238 
Pyramid, the Great, 18 



Pythagoras (lunar crater), 235 
Pyxis, 277, 312, Maps V, XIV 

Quadrans Mutatis, 154 
Quadrati tids, 15+ 
Quasars, 202-3, 20 ^» 3" 

R Corona: 185, 334 

R Cygni, 338-9 

R Leonis, 330-1 

R Lyras, 324 

R Scuti, 185, 326-7 

R-stars, 164-g 

Radar astronomy, 3a, 106 

Radar detection of meteors, see Meteors 

Radar measures of Venus, see Venus_ 

Radial motions of stars, see Stars, radial 

motions of 
Radioactivity, 13 

Radio astronomy, 3a, 169, 206, 335-6 
Radio sources, 169 
Radio telescopes, 31, 309-1 1 
Ranger vehicles, 79-80, 235 
Reber, G., 32, 309 
Reflecting telescopes, set Telescopes, 

Refracting telescopes, set Telescopes, 

Refraction, 33-6 

Rcgiomoncanus (lunar crater), 238 
Regulus, 265, 279 

occultations by Moon, 88 

occultation by Venus, 90 
Reichenbach (lunar crater), 233 
Reticulum, 314, Map XV 
Reversing Layer, solar, 64 
Rhea, 131 

Rheita (lunar crater), 232-3 
Rho Cassiopeia:, 327 
Riccioli (lunar crater), 237 
Ridley, H. B., 149, 152 
Rigel, 156, 157, 160, 164, 271 
Right ascension, 41, 155-6 
Ring Nebula in Lyra, 194-5, S87 
Ringsdore, P., 86 
Riphzan Mountains (lunar), 235 
Ritter (lunar crater), 231 
Rocket astronomy, 33 
Remcr, Ole, 28 
Rook Mountains (lunar), 235 
Rons, Sinus, 233 
Rosse, Lord, 31 

RR Lyra; Variables, see Variable Stars 
Ryle, M„ 206 

S DoradQs, 199 
S-stars, 164-5 
SS Cygni, 185, 330 
Sabine (lunar crater), 231 
Sagitta, 288, Map VIII 

Sagittarius 289, Map VIII, 307, Map 

Saiph, 271 

Saros, the, 92 

Sartory, P. K., 85 

Satellites, artificial, 222-3 

Satellites of planets, tables of, 210-11 

Saturn, 17, 21, 50.52, 5 8 > 128-31 
dimensions and mass, 128 
intensities, estimating, 128, 209 
methods of observing, 131, 209 
oppositions of, 216 
rings of, [28-30 
satellites of, 131 
surface markings on, 128 
temperatures 01), 128 
White Spot of 1933, 13, 128 

Sceptrum Brandenburg! cum, 154 

Schiaparelli, G. V., 115 

Schickard (lunar crater), 238 

Schmitt, Dr. H., 8t 

Schroter, J. H., 29, 120 

Schroter Effect, 1 10 

Schwabe, H., 67 

Scoresby (lunar crater), 231 

Scorpio, 293, 295, Map IX, 308, Map 

Sculptor, 297, Maps X, XV 

Scutum, 289, Map VIII 

Secchi, Father, 163 

Secular variables, see Variable Stars 

Sellers, F. J., 66, 71 

Serenitatis, Mare, 228 

Serpens, 289, 295, Maps VIII, IX 

Sextans, 278, Map V 

Shadow Bands, 97 

Shell stars, 1C8 

Shepard, A., 81 

Shklovsky, L, 1 18 

Siderites and Sidcxolites, 1 52 

Sidgwick.J. B., 117 

Si nope, lai 

Sirius, 156, 157, 160, 163, 164, 172, 

'74-5. 275. 3° ' 

Companion of, 172, 174-5 
Sirsalis (lunar crater), 238 
Skylab, 49, 144 
Slow motions, 41 
Smythii, Mare, 229 
Societies, astronomical, 339-40 
Solar System, the, 28, 50-61 tao, 

bodies in, 50 

origin of, 204-5 

scale model of, 30, 50 
South Africa, sky from, 300-19 
South Tropical Disturbance, see Jupiter 
Southern Cross, see Crux Australis 
Space-flight, 7 
Spectrohcliograph, 65 
Spectrohelioscope, 65 



Spectroscope, development of, 29, 63 
Spica, 266, 279, 301 

occultations of, 88 
"Spiral Nebula;", see Galaxies 
Scorer's Law, 68 
Sputniks, Russian, 33 
Star clusters, set Clusters, star 
Stars, 17, ai, 29-30, 154-90 

binary, see Binary stars 

distances of go, 50, 158-60, 183 

double, see Double Stars 

evolution of, 165-7 

first-magnitude, list of, 251 

flare, set Flare stars 

fiant and dwarf, 165 
igh-velocity, 198 

least massive, 168 

luminosities of, 160 

magnitudes, apparent, 157-8, 252-3 

masses of, 167-8, 17a 

multiple, see Multiple stars 

nomenclature of, 157 

parallaxes of, 158-9, 1 70 

populations, see Populations, stellar 

proper motions of, 161 

proper names, list of, 244-50 

radial motions of, 161 

radio, set Radio sources 

shell, see Shell stars 

sizes of, 165, 167 

source of energy of, 166-7 

spectra of, 16 1 

spectral types of, 163-6, 254 

supcrgiant, 169 

temperatures of, 160, 164 

variable, see Variable stars 

White Dwarf, see White Dwarfs 
Steady-state theory, 205-6 
Steinheil (lunar crater), 233 
Step-Method, Pogson's, 186-7 
S termer, C, 100 
Straight Range (lunar), 235 
Straight Wall (lunar), 338 
Sun, the, 17, 31, 30, 50, 62-72 

constitution of, 6a 

density of, 62 

dimensions and mass of, 62 

discovery of helium in, 15 

evolution of, 166 

magnitude of, 158 

methods of observing, 62, 69-72 

motion in Galaxy, ig8 

photography of, 7a 

spectrum of, 29, 63-5, 164 

surface gravity on, 62 

temperature of interior, 63-4 

temperature of surface, 62 
Sun-caps, danger of using, 70 
Suntpots, 63, 65-70, 7a 

apparent movements of, 67-8 

brilliance of, 66 

cycle of, 67-9 

groups of, 66 

magnetic fields of, 68-9 

nature of, 66 

of April 1947, 67 

of June-December 1943, 66 

structure of, 66 

temperatures of, 66 

weather, suggested connections with, 
Supernova in Andromeda Galaxy, 200 
Supernova;, 169, 189 
Swigert, A., 81 
Syene, ai 

Synodic periods of planets, 58 
Syrtis Major, 116 

T.L.P.S (Transient Lunar Pheno- 
mena), 85-7 
Tarun tius (lunar crater), 231 
Taurus, 374, Map IV 
Telescopes, reflecting, 27, 37-40 

Casscgrain, principle of, 38 

constructing, 39-40 

Gregorian, principle of, 38 

Hcrschelian, principle of, 38 

at Herstmonceux, 32, 48 

at Mount Wilson, 32, 48 

Newtonian, principle of, 37 

Newton's, 26-7 

at Palomar, 32, 47, 163 

Rosse 's, 31 
Telescopes, refracting, 25-6 

at Lowell Observatory, 49 

at Mcudon, 48, 117, 224 

at Pic du Midi, 48 

principle of, 35 

at Yerkes, 36, 48 
Telescopes, care of, 44-6 

choosing, 42-4, 46 

mountings for, set Mountings, tele- 
Telescopium, 308, Map XIII 
Tethys, 131 
Thales, 19, 20 
Thebit (lunar crater), 238 
Theophilus (lunar crater), 233 
Theta Eridani, 188, 274, 314 
Theta Ononis, 195, 273 
Thuban, 18 
Tiberius, Emperor, 99 
Timocharis (lunar crater), 235 
Titan, 131 
Titania, 133 
Tombaugh, C, 134 
Tranquil] i talis, Mare, 81, 228 
Transits of Mercury and Venus, see 
Mercury and Venus 



Trapezium, the, see The [a Orionis 
Triangulum, 285, Map VII 

Spiral in, 201, 385 
Triangulum Australc, 306, Map XIII 
Trigonometry, invention of by Hip- 

p arc I) us, 22 
Triton, 134 

Trojans, set Minor Planets, Trojan 
Tucana, 316, 317, Map XVI 
Twinkling of planets, 57 
Tycho Brahe, 23-5 
Tycho (lunar crater), 79, 8a, 93, 338 

U Cygni, 323 

U Delphini, 325 

U Geminorum, 185, 33 1 

U Orionis, 33a 

UV Ceti, 32 a 

UW Orionis, 331 

Umbriel, 133 

Universe, age of, 204-3 

evolution of, 305-7 

future of, 905-7 

origin of, 204-5 
Uramborg, 94 
Uranium, 13, 63 
Uranus, 98, 131-4 

dimensions and mass, 139 

discovery of, 131 

inclination of axis of, 13a 

methods of observing, 1 32-3 

rings, 133 

satellites of, 133 
Ursa Major, 154, 158, 170, 269, Map 

Ursa Minor, 158, 2G9, Map III 
Ussher, Archbishop, 204 

Vatlcs Marineris, 1 15 
Van de Kamp, P., 168 
Vaporum, Marc, 228 
Variable Stan, 14, 178-90 

binocular, 324-7 

Cepheid, 178, 182-3, 900, 391 

eclipsing, 178-81, 330 

irregular, 178, 184-5, 39' 

light-curves of, 181 

long- period, 183-4, 3 31 

methods of observing, 1 85-7, 330-3 

R Cororae Boreal is type, 185, 392 

RR Lyre type, 178, 183, 193, 320 

RV Tauri type, 185, 321 

secular, 187-8 

semi-regular, 321 

T Taun type, 322 

types of, 178 

U Geminorum type, 185, 33 1 

W Virginis type, 321 

Z Camelopardalis type, 33a 
Vega, 156, 266, 386 
Vela, 309-10, Map XIV 
Vendelinus (lunar crater), 333 
Veneras g and io,iog 
Venus, 17, at, 26, 50-1, 52, 61 , 90, 97, 
108-13, 156 

atmosphere of, 108, 109 

axial rotation of, 108-9 

dichotomy of, 108-10 

elongations of, 919 

magnitude of, 1 58 

methods of observing, 109-1 1 

occupations by, 00 

phases of, 36, 55-7, 1 m 

radar echoes from, 33, 54 

rotation of, 1 09 

surface details on, 1 08, 1 09 

transits of, 312 
Venus 7, tog 
Vernal Equinox, see Aries, First Point 

Vesta, 59, 120 
Vikings I and 3, 61, 1 16 
Virgo, 379-81, Map VI, 300, 301 
Vitello (lunar crater), 338 
Vlacq (lunar crater), 233 
Volans, 312, Map XIV 
Von Zach, F. X., tao 
Vulpecula, 388, Map VIII 

W Cygni, 326 

W-stars, 164 

Walter (lunar crater) , 338 

Wargentin (lunar crater), 238 

VVatt (lunar crater), 233 

Wedges, solar, 70 

Werner (lunar crater), 333 

Whipple, F. L., 138 

Whitaker, E. A., 224 

White Dwarfs, 166-7 

Wild Duck Cluster, 289 

Wilhelm Humboldt (lunar crater), 933 

Wilson Effect, 73 

Wolf, 359, 160, 165 

Wolf-Rayet stars, 164, 165, 166, 194 

Wollaston, W. H„ 63 

Wren, Sir Christopher, 97, 48 

X-rays, ig6 

Zenith, the, lot 

Zcta Argus, 1 64 

Zeta Auriga, 180 

Zcta Ursa: Majoris, set Mizar 

Zodiac, the, 51 

Zodiacal Light, the, 109-3, '48 



Other tides by Patrick Moore 


''This new compendium, edited by Patrick Moore, 
will be warmly welcomed. Separate chapters arc 
devoted to observations of the sun and moon and 
to each planet in turn; other topics, each in itself 
suitable for amateur observation, include the minor 
planets, comets, meteors, the aurora, double and 
variable stars." — Times Literary Supplement. 


I'atrick Moore describes what astronomy is all 
about and then takes the main features of the 
heavens, providing simple means of recognition and 
much detailed information about what can be seen. 


"It is as a lunar observer of international note, and 
a reporter who has been closely involved with the 
coverage of lunar exploration throughout the space 
age, that Moore speaks with authority on the 
radically changed views about our natural satellite 
over the past two decades. 
"This is Moore at his classic best." — New Scientist. 


"Guide to the Stars reminds us, in no uncertain way. 
just why the name of Patrick Moore has achieved 
such importance in the popularisation of astronomy. 
Here he is on familiar ground, and the text is 
both a good read and informative no mean 
achievement." — New Scientist. 


"A generally excellent text at the introductory 
level." — Nature. 


This is the first full-length description of Mars to 
be written since the Viking landings of 197(>. h 
has meant that for the first time we have been able 
to take into account the important evidence of 
close-up photography and scientific experiments 
conducted on the surface. The world revealed, with 
the help of diagrams and photographs, is an en- 
thralling one. 



Astronomy as a Hobby 

The Unfolding Universe 

Telescopes and Observatories 

The Solar System 

The Sun 

The Moon 

Occultations and Eclipses 

Aurora and the Zodiacal Light 

The Nearer Planets 

The Outer Planets 
Comets and Meteors 
The Stellar Heavens 
The Nature of a Star 
Double Stars 
Variable Stars 
Star-Clusters and Nebula; 
The Galaxies of Space 
Beginnings and Endings 





Planetary Data 
Satellite Data 
Minor Planet Drama 
Elongations and Transits of the 

Inferior Planets, 1970 80 
Map of Mars 

Oppositions of Planets, 1970-80 
Jupiter: Transit Work 
Saturn: Intensity Estimates 
Forthcoming Eclipses 
Artificial Satellites 
Lunar Detail visible with 

Different Apertures 
The Lunar Maps 
Important Periodic Corneas 
Annual Meteor Showers 
The Constellations 


r Names of Stars 

Stars of the First Magnitude 
Standard Stars for Each 

The Greek Alphabet 
Stellar Spectra 
Magnitudes and Separations 

for Various Apertures 
Angular Measure 
Lest Double Stars 
Naked- Eye Nova; 
Messier' s Catalogue 
The Star Maps 
The Observation of Variable 

Radio Astronomy 
Amateur Observatories 
Astronomical Societies 

9 th